Taxonomy and morphology of three species of Psammobatis distributed in the Southwestern Atlantic Ocean (Rajiformes: Arhynchobatidae) with notes on intraspecific variation

Evelyn F. Santiago¹ and Karla D. A. Soares¹

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Abstract​

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Introduction​

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Batoids are the most diverse group of cartilaginous fishes, distributed in four orders: Rajiformes, Torpediniformes, Rhinopristiformes, and Myliobatiformes. Rajiformes represents almost half of batoid diversity, comprising about 300 valid species (Last et al., 2016; Weigmann, Reinecke, 2023; Fricke et al., 2024). Representatives of this order are classified into four families (Rajidae, Arhynchobatidae, Gurgesiellidae, and Anacanthobatidae) whose characterization and differentiation mainly based on external morphology is compromised by the overall similarity among their representatives (Gomes et al., 2019).

Psammobatis Günther, 1870 belongs to Arhynchobatidae (McEachran, 1983; Last et al., 2016) and is endemic to South America, with seven valid species distributed in the Atlantic and Pacific oceans (McEachran, 1983; Carvalho, Figueiredo, 1994; Mabragaña et al., 2020). Psammobatis rudis Günther, 1870 and P. normani McEachran, 1983 are found in the Southwest Atlantic Ocean (SWA) and the Southeast Pacific Ocean (SEP); P. scobina (Philippi, 1857) is endemic to SEP, and the four remaining species occur exclusively in the SWA: P. bergi Marini, 1932, P. extenta (Garman, 1913), P. lentiginosa McEachran, 1983 and P. rutrum Jordan, 1891 (Paragó, 2001; Mabragaña et al., 2020). The last four species have been recorded along the Brazilian coast.

The taxonomic history of Psammobatis is complex. Regarding Brazilian species, only P. bergi is easily distinguishable from its congeners, while the other three species are often misidentified due to their overall similarity. The first descriptions of P. rutrum and P. extenta did not provide illustrations or relevant diagnostic characters to differentiate them, which led to several misidentifications (e.g., Miranda Ribeiro, 1907; Figueiredo, 1977; Roux, 1979). Later, McEachran (1983) provided more morphological data for Psammobatis species and also described two new species, P. lentiginosa and P. glansdissimilis McEachran, 1983. Carvalho, Figueiredo (1994) synonymized the species described by Miranda Ribeiro (1907), Garman (1913), and P. glansdissimilis with P. extenta, based on similarities in dermal denticles along the spermatic groove of male specimens.

Paragó (2001) and Gomes (2002) presented taxonomic keys to distinguish Psammobatis from Brazil, using mainly coloration data and dermal denticles. Most characters used in those keys are observed only in males (dermal denticles on the clasper of P. extenta) and others only in females (prickles on the pelvic fin of P. lentiginosa) (Paragó, 2001; Gomes, 2002; Gomes et al., 2019), highlighting the need to consider intra- and interspecific variation in order to improve species identification.

Therefore, this study aims to review the taxonomy of P. extenta, P. lentiginosa and P. rutrum, redescribing and illustrating internal and external morphological characters that could be used to unequivocally distinguish these species. Information on the ontogenetic, sexual and individual variation of each species is also presented.

Material and methods

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A total of 104 specimens were examined (59 of Psammobatis extenta, 23 P. lentiginosa and 22 P. rutrum) collected in Brazilian waters, between the states of Rio de Janeiro and Rio Grande do Sul. Specimens are preserved in 70% alcohol and deposited in the ichthyological collections of the Museu Nacional, Rio de Janeiro (MNRJ), Universidade do Estado do Rio de Janeiro (DBAV.UERJ/Ichthyological Collection and AC.DBAV.UERJ/Anatomical Collection of Chondrichthyes) and the Museu de Zoologia da Universidade de São Paulo (MZUSP). Some specimens recently collected by the DEEP-OCEAN project (supervised by Dr. Marcelo Melo, IO-USP) were also examined herein. Material examined is listed along each species description.

For each individual, we verified the capture locality when available and the sex according to the presence or absence of claspers. Maturity stages were assessed according to size at maturity as mentioned in McEachran (1983), Braccini, Chiaramonte (2002), Mabragaña et al. (2012) and Martins, Oddone (2017).

Skin samples from nine regions in 11 specimens were removed to visualize dermal denticles using a scanning electron microscope (SEM), including two adults (male and female) and three immatures (two males and one female) of P. extenta; one adult male and three immatures (one male and two females) of P. rutrum (two males and two females); one adult male and one immature female of P. lentiginosa. All these specimens are marked with an asterisk along the lists of material examined. Tissue samples were removed using a scalpel and preserved in 70% alcohol before their preparation in stubs. Samples were then metallized with a gold layer at the Laboratório de Ultraestrutura Celular Hertha Meyer (LUCHM), located at the Centro de Pesquisa em Medicina de Precisão (CPMP) in the Universidade Federal do Rio de Janeiro (UFRJ). SEM-images were taken using microscopes Zeiss EVO 10 and Fei Quanta 250 at the Centro Nacional de Biologia Estrutural e Bioimagem (CENABIO/UFRJ).

The terminology used to describe dermal denticles and other external morphological characters follows Leible (1988), Paragó (2001), and Gravendeel et al. (2002). Dermal denticles were identified and counted according to each body region (Fig. 1), following Leible (1988).

FIGURE 1| Spinulation pattern of Psammobatis species. A. P. extenta. B. P. lentiginosa. C. P. rutrum. Modified from Gomes et al. (2019). alt, alar; clt, caudo-lateral; dd, dermal denticles.; dlt, dorsolateral; iot, interorbital; mct, mid-caudal; mdt, middorsal; mlt, malar; mot, midorbital; mpt, mid-pectoral; nut, nuchal; pck, prickles; pct, pectoral; pet, preorbital; plt, pelvic; pot, postorbital; ppt, posterior-pectoral;rst, rostral; sct, scapular; spt, spiracular.

Eighty-two specimens were measured (37 of P. extenta, 22 of P. lentiginosa and 23 of P. rutrum)with the aid of a caliper with a precision of 0.05 mm for measurements up to 150 mm and a tape measure with accuracy of 1 mm. Total length (TL), disc width (DW), and derivative measurements were collected with the tape stretched on a flat surface where the specimen was deposited, with a straightened tail. Of the measurements used, 22 were adopted from Leible (1988) and Hubbs, Ishiyama (1968), while the “disc width at eye line” (DWE) is proposed here as new, totaling 23 measurements (Fig. 2). This measurement was proposed to better assess differences between males and females regarding the disc shape at the eye level.

FIGURE 2| Measurements for morphometry data. Modified from Gomes et al. (2019). CL, caudal length; CLB, clasper base width; CLI, clasper inner length; CLO, clasper outer length; DGS1, distance between first gill slits; DGS5, distance between fifth gill slits; DL, disc length; DW, disc width; DWE, disc width at eye line; EYD, eye diameter; FDC, distance from first dorsal fin origin to posterior end of caudal fin; GS1, first gill slit width; GS3, third gill slit width; GS5, fifth gill slit width; INO, interorbital distance; INW, internasal distance; MOW, mouth width; PFD, distance from posterior margin of pelvic fin to first dorsal fin origin; PNR, prenasal length; POB, preorbital length; POR, preoral length; SVL, snout-vent length; TL, total length.

For descriptive purposes, absolute values of the morphometric measurements were transformed into body proportions expressed as a percentage of disc width (%DW). For data analysis, according to Lleonart et al. (2000), a normalization technique was used to scale data showing allometric growth. Total length (TL) was used as the independent variable, while the other 22 morphometric measurements were considered dependent variables. TL₀ represents a reference size of value (236.09 mm for this study) to which all specimens were reduced (or amplified) (Lombarte, Lleonart, 1993; González-Castro et al., 2016; Gabbanelli et al., 2018). The standardized values organized by sex and total sample of each species were used to verify the normality and homogeneity of groups using the Shapiro-Wilk test (α = 0.05) and Levene’s test (α = 0.05), respectively. Due to the low n-sample size from each locality, no comparisons of morphometric data were made between localities. Then, to investigate differences between males and females, the Student’s t-test (α = 0.05) was applied to variables with a normal distribution and the Man-Whitney test (α = 0.05) to those that were not normal. For the differences between species, the Kruskal-Wallis test was applied, with a significance level of 0.05. Dunn’s post hoc test (α = 0.05) was then used to identify group differences.

Neurocranium and clasper of at least one individual of each species were dissected manually using scalpels and forceps to describe the internal components. The right clasper was chosen for analysis of the external morphology, while the left clasper was dissected for analysis of the skeleton. The terminology used for the clasper structures was based on McEachran (1983), Menni (1972), Moreira et al. (2017) and Moreira (2017), and for the neurocranium, McEachran (1983), Leible (1988), and Soares et al. (2021).

Data was compiled in Microsoft Excel software and analyzed in the R Studio (v. 4.4.2). Normalization was done using the “allomr” package (v. 0.3.0); the statistical description was carried out using the “psych” package (v. 2.3.3); for the Shapiro-Wilk and Dunn post-hoc tests, the “rstatix” package (v. 0.7.2) was used; for the Levene test, the “car” package (v. 3. 1–2); the outlier check was carried out using the “graphics” package (v. 4.3.0); the Student’s t-test, Man-Whitney and Kruskal-Wallis tests were carried out using the “stats” package (v. 4.3.0). Significant values for each test are presented as supplementary material.

Image editing was performed with the aid of Adobe Photoshop CS6 and scales were created in the ImageJ program. The distribution map was generated with the aid of Google Earth and Quantum Gis program (v. QGIS3.28LTR), based on the locality, latitude, and longitude data, when available, following Calegari et al. (2016).

Results​

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Psammobatis extenta (Garman, 1913)

Raja erinacea (non Mitchill). — Miranda Ribeiro, 1907:176, pl. XII, XIII (Rio de Janeiro, Brazil; catalogue).

Raia extenta Garman, 1913:356 (original description; type-locality: off the coast of Ilha Rasa, Rio de Janeiro, Brazil).

Psammobatis extenta —Fowler, 1942:131 (Brazil; listed). —Menni, 1972 (clasper morphology). —Carvalho, Figueiredo, 1994 (systematic study and lectotype selection). — McEachran, Dunn, 1998:286 (systematic study). —Mazzoleni, Schwingel, 1999:114 (Itajaí, Santa Catarina, Brazil; listed). —Compagno, 1999:489 (listed). —Cousseau et al., 2000:30 (Argentina and Uruguay; catalogue). —Menni, Stehmann, 2000:87 (Argentina, Uruguay and Brazil; listed). —Muto et al., 2001 (Ubatuba, São Paulo, Brazil; diet). —Paragó, 2001 (systematic study). —Gomes, 2002 (systematic study). —Braccini, Chiaramonte, 2002 (Argentina; reproductive biology). —Braccini, Chiaramonte, 2005 (Argentina; morphometry). —Gomes, Gadig, 2003:29 (São Paulo, Brazil; listed). —Mabragaña, 2007 (Argentina; biological and ecological study). —Cousseau et al., 2007:62 (Mar del Plata, Argentina; catalogue). —Rocha et al., 2010 (egg capsules). —Weigmann, 2016:100 (listed). —Last et al., 2016:457 (listed). —Nión et al., 2016:23 (Uruguay; listed). —Viana et al., 2017:3 (Rio de Janeiro, Brazil; diet). —Cordeiro, Oddone, 2019:47 (Rio Grande do Sul, Brazil; reproductive biology). —Gomes et al., 2019:299, fig. 291 (Rio de Janeiro, Brazil; catalogue). —Brum-Neto, Lucena, 2020 (Brazil; tooth morphology). —Sabadin et al., 2020:1901 (Argentina, Uruguay and Brazil; listed). —Mabragaña, Cousseau, 2021:64 (Argentina; listed). —Hoff et al., 2023 (Brazil; listed).

Psammobatis sp. —Figueiredo, 1977:34, fig. 75 (Southern Brazil; catalogue).

Psammobatis glansdissimilis —McEachran, 1983:67, fig. 18 (systematic study). —Mazzoleni, Schwingel, 1999 (Itajaí, Santa Catarina, Brazil; listed). —Menni, Stehmann, 2000:87 (Argentina, Uruguay and Brazil; listed).

Diagnosis. Psammobatis extenta is distinguished from P. lentiginosa and P. rutrum by the dark brown coloration pattern of tiny dark spots (vs. black in P. lentiginosa and whitish in P. rutrum); tiny spots distributed around the orbits (vs. absent in P. lentiginosa and concentrated in the preorbital region in P. rutrum); presence of thorns on pectoral fins (vs. reduced or absent in P. lentiginosa);pectoral thorns with tip oriented towards the caudal region (vs. tip oriented towards the lateral margin of disc in P. rutrum); presence of a mid-pectoral thorn (vs. absent in P. lentiginosa and P. rutrum); continuous rows of dorsal thorns posterior to the scapular region (vs. interruption only from the middorsal to the pelvic insertion in P. lentiginosa and interruption of the three rows in P. rutrum); spermatic groove of claspers positioned dorsally with dermal denticles (vs. lateral spermatic groove and denticles absent in P. lentiginosa and P. rutrum); presence of ocelli on the posterior region of pectoral fins in adults and juveniles (vs. absent in P. lentiginosa and P. rutrum); anterior fontanelle rectangular (vs. trapezoidal in P. rutrum and P. lentiginosa); basal fenestrae rectangular and narrow (vs. kidney-shaped in P. rutrum and P. lentiginosa); posterior nasal cartilage perpendicular in relation the anteroposterior axis (vs. oblique in relation the anteroposterior axis in P. rutrum); dorsal terminal cartilage 2 and accessory terminal cartilage 2 absent (vs. present in P. lentiginosa and P. rutrum); accessory terminal cartilage 1 continuous with the ventral marginal cartilage (vs. articulated in P. lentiginosa and P. rutrum).

External description. Disc 1.4–1.5 times wider than long (Tab. 1). Heart-shaped disc in juvenile and adult specimens; subtle in the former and accentuated in the latter. Adults with wide pectoral fins and convex margins in the posterior region, while the anterior region narrows towards the snout. Adult males with concave anterior disc margin close to the orbital region; disc width at eye line in females is 1.2 times longer than in males.

TABLE 1 | Morphometric measurements for males and females of Psammobatis extenta. Disc width (DW) in millimeters and other measurements as percentages of disc width (% DW). CL, caudal length; DGS1, distance between first gill slits; DGS5, distance between fifth gill slits; DL, disc length; DWE, disc width at eye line; EYD, eye diameter; FDC, distance from first dorsal fin origin to posterior end of caudal fin; GS1, first gill slit width; GS3, third gill slit width; GS5, fifth gill slit width; INO, interorbital distance; INW, internasal distance; MOW, mouth width; PFD, distance from posterior margin of pelvic fin to first dorsal fin origin; PNR, prenasal length; POB, preorbital length; POR, preoral length; SVL, snout-vent length; TL, total length.

Measurements	Females			Males
	Mean	Range	N	Mean	Range	N
TL	179.6	163.4–204.6	19	177.7	160.8–201.1	18
DW	113.7	61.9–152.0	19	122.6	77.9–153.0	18
CL	100.5	89.5–112.6	19	101.3	82.8–121.7	18
DL	82.5	75.4–91.7	19	80.2	68.4–90.5	18
POB	18.4	13.6–21.3	19	17.1	11.9–19.9	18
PNR	14.5	9.7–19.4	19	12.6	7.9–15.6	18
INW	7.1	5.3–9.5	19	7.1	5.4–9.2	18
EYD	5.1	4.0–6.1	19	5.7	4.1–7.3	18
INO	7.0	5.9–9.0	19	6.8	3.4–8.6	18
POR	19.4	13.6–24.1	19	17.5	13.8–21.2	18
SVL	74.2	67.9–82.3	18	73.4	66.1–99.9	18
MOW	12.1	9.4–13.9	19	12.6	10.5–15.3	18
FDC	26.1	22.6–30.3	19	26.0	19.1–32.5	17
PFD	57.0	48.9–75.1	19	56.3	43.4–75.8	17
GS1	3.3	2.2–4.4	14	3.3	2.4–3.9	15
GS3	3.2	2.4–3.7	14	3.2	2.6–4.0	15
GS5	2.5	1.8–3.5	13	2.6	1.8–3.7	14
DGS1	24.7	19.3–27.4	16	24.3	21.3–28.2	16
DGS5	13.4	8.6–15.6	15	11.1	9.4–13.4	15
DWE	60.8	50.7–72.0	19	52.4	43.0–66.7	18

Preorbital length 3.0–3.6 times the eye horizontal diameter and 2.5–2.6 times the interorbital distance. Preoral length 1.4–1.6 times the mouth width. Upper jaw arched, especially in middle region; lower jaw convex. First pair of gill openings 1.3 times larger than the fifth. Distance between first gill slits 1.8–2.2 times the distance between the fifth.

Pelvic fins convex externally with a notch forming anterior and posterior lobes. Pelvic anterior lobe shorter with a convex anterior margin; posterior margin distinguished by radial tips and continuously connected to the lateral margin of posterior lobe. Posterior lobe with a convex lateral margin and a straight inner margin. Dorsal fins similar in size and shape, with rounded apex. Distance from pelvic posterior margin to origin of first dorsal fin 2.2 times the distance from first dorsal origin to posterior margin of caudal fin. Tail long, 1.7–1.8 times in total length and 1.4 times the snout-vent distance. Caudal fin rounded.

Coloration in alcohol. Dorsal coloration dark brown, its intensity varying according to development stage (Fig. 3A). In adults, a grouping of tiny dark spots distributed over the dorsal surface produces a reticulated appearance, contributing to the darkening of this region. Spots can still form circular borders, smaller or equal to the eye diameter. Preorbital region with a lighter triangular area contrasting to the predominant background color and tiny spots distributed around the orbits, projecting towards disc margin (Fig. 4A). An ocellus is observed near the posterior region of each pectoral fin in both adults and juveniles (Figs. 3A, 5A). In juveniles, a dark spot located in the central region of each pectoral fin and a cluster of dark spots located on the posterior region of each pectoral fin as in P. rutrum, but spots can be less intensely colored (Figs. 3E, 5A). Some specimens present a black spot on the snout tip as in P. lentiginosa and P. rutrum (Figs. 3A, C, E). Tail region presenting the same predominant background color, but also with lighter bands formed by the union of spots on dorsal region. In adults, some bands form an hourglass. Ventral region uniformly cream (Fig. 3B).

FIGURE 3| Color pattern of adult individuals. A. Dorsal view of Psammobatis extenta, MNRJ 32323, female, 267 mm TL and B. Ventral view of MNRJ 32323, female, 252 mm TL. C. Dorsal view and D. Ventral view of P. lentiginosa, MZUSP 127759, male, 306 mm TL. E. Dorsal view and F. ventral view of P. rutrum, MZUSP 45151, female, 247 mm TL. Scale bars = 5 cm.

FIGURE 4| Dermal denticles and coloration of Psammobatis species, dorsal body surface. A. Head and D. Central dorsal region of P. extenta, MNRJ 32323, female, 267 mm TL. B. Head and E. Central dorsal region of P. lentiginosa, MNRJ 127759, male, 406 mm TL. C. Head and F. Central dorsal region of P. rutrum, UERJ 9954, female, 242 mm TL. Scale bars = 10 mm.

FIGURE 5| Color pattern of immature individuals. A. Dorsal view of Psammobatis extenta, MNRJ 32323, female, 125 mm TL. B. Dorsal view of P. lentiginosa, MZUSP 127759, female, 118 mm TL. C. Dorsal view of P. rutrum, MZUSP 45151, female, 128 mm TL. Scale bars = 3 cm.

Dermal denticles. Rostral and malar thorns forming rows with no differences between sexes; star-shaped base and a curved crown that narrows towards its distal end (Figs. 6C–D). Rows of alar thorns of adult males situated posterior to the malars and positioned horizontally, close to pectoral lateral margin, with distal end oriented medially; elongated base and a thorn-shaped crown, arranged in two to six alternating rows, five to 20 denticles (Fig. 6A; Tab. 2).

FIGURE 6| Dermal denticles of Psammobatis extenta from specimens DBAV.UERJ 1545, immature male, 241 mm TL (A) and DBAV.UERJ uncatalogued, adult male, 262 mm TL (B, C, D, E, F). A. Alar thorns. B. Posterior-pectoral thorns. C. Malar thorns. D. Rostral thorns. E. Nuchal thorns. F. Scapular thorns. Scale bars A, B, F = 200 µm; C, D, E = 1 mm. Anter, anterior region; Post, posterior region.

TABLE 2 | Meristic counts of thorns of Psammobatis extenta, P. rutrum and P. lentiginosa.

Thorns	P. extenta (f = 13; m= 8)	P. lentiginosa (f = 7; m = 5)	P. rutrum (f = 9; m = 7)
Preorbital	2–5	1–4	1–5
Midorbital	0–3	0–2	1–3
Postorbital	0–2	0–2	0–2
Spiracular	2–4	0–4	1–4
Nuchal	1–3	1–3	1–3
Scapular	5–21	3–16	5–17
Alar (rows)	2–6	1–3	3–5
Middorsal/mid-caudal	26–39	26–54	15–34

Head with two to five preorbital thorns, none to three midorbital thorns, none to two postorbital thorns, and two to four spiracular thorns. Thorns similar in structure to the nuchal and scapular but smaller. Nuchal and scapular thorns forming a triangular grouping, organized into one to three nuchal thorns and five to 21 scapular thorns. Scapular thorns more concentrated in the central region, resulting in a smaller base for the triangle; leaf-shaped base with shallow grooves and a curved crown with an extremely sharp distal end (Figs. 6E–F).

Mid-pectoral thorns located on the medial region of each pectoral fin. Stellate base with well-defined grooves between the dorsal ridges, a slightly curved crown, and a tapered distal end with a straight orientation; occurring individually or grouped into two to four thorns (Figs. 7A–B). Smaller, cross-shaped dermal denticles with a tapered distal end around the mid-pectoral thorns, giving a rough texture to this region. Posterior pectoral thorns present in both males and females; cross-shaped or star-shaped base, with a curved crown and tapered distal end (Fig. 6B).

FIGURE 7| Mid-pectoral thorns of Psammobatis extenta (A, B) e pectoral thorns of P. rutrum (C, D). A. DBAV.UERJ 2144.2, adult female, 275 mm TL. B. DBAV.UERJ uncatalogued, adult male, 262 mm TL. C. DBAV.UERJ 848.3, immature female, 230mm TL. D. DBAV.UERJ 2130, adult male, 251 mm TL. Scale bars A, B = 1 mm; C, D = 200 µm. Anter, anterior region; Post, posterior region.

Well-developed dermal denticles located along the margin of clasper spermatic groove (Fig. 8A). Middorsal row of thorns presenting or not a small interruption, while dorsolateral rows extend to the tail region, although there is considerable individual variation in this pattern (Fig. 4D). Middorsal and dorsolateral thorns similar in structure to the nuchal and scapular ones. Smaller denticles present posteriorly to the scapula and adjacent to thorn rows, giving a rough texture to this region. Cross-shaped or plateau-like bases and crown curved with a tapered distal end.

FIGURE 8| Clasper of Psammobatis species. A. P. extenta, DBAV.UERJ 2127, 258 mm CT, male, Angra dos Reis, RJ. The arrow points to the spermatic groove with dermal denticles. B. P. lentiginosa MZUSP 86551, male, 315 mm TL, Santa Catarina, SC. C. P. rutrum, MZUSP 45152, male, 240 mm TL, Rio Grande do Sul, RS. Scale bars = 10 mm.

One row of mid-caudal thorns and two caudo-lateral thorns, one at each side of the tail, all oriented anteroposteriorly; denticles arranged randomly between rows. Caudo-lateral thorns with base and crown flattened dorsolaterally. Mid-caudal thorns similar in structure to middorsal thorns and forming a continuous row with them, 26 to 39 denticles (Tab. 2).

Geographical distribution. Examined specimens with a wide geographical distribution, extending along the coasts of Rio de Janeiro, São Paulo, Paraná, and Santa Catarina (Fig. 9). This species is also recorded in the Gulf of San Jorge, Argentina (Mabragaña, 2007).

FIGURE 9| Map of southeastern South America showing the geographical distribution based on the localities where the specimens examined were collected. Psammobatis extenta (yellow), P. lentiginosa (red), P. rutrum (blue). Filled circles, no geographic coordinates; empty circles, geographic coordinate data. Triangles, type-species location.

Material examined. MNRJ 12317, lectotype. MNRJ 12318, paralectotype, 4, off the coast of Ilha Rasa, Rio de Janeiro, Brazil, 23°S 43°W. Santa Catarina: DBAV.UERJ 1545*, male, 241 mm TL, 110 mm DW, Itajaí. DBAV.UERJ 1624.7, male, 190 mm TL, 94.5 mm DW, DBAV.UERJ 1624.11, female, 196 mm TL, 111 mm DW, DBAV.UERJ 1624.12, male, 180 mm TL, 94 mm DW, DBAV.UERJ 1624.14, female, 180 mm TL, 107 mm DW, DBAV.UERJ 1624.16, male, 200 mm TL, 111 mm DW, DBAV.UERJ 1624.17*, male, 184 mm TL, 107 mm DW, DBAV.UERJ 1624.18, female, 230 mm TL, 126 mm DW, DBAV.UERJ 1624.19, female, 220 mm TL, 118 mm DW, DBAV.UERJ 1624.20, male, 225 mm TL, 127 mm DW, São Francisco do Sul. São Paulo: DBAV.UERJ 883, female, 256 mm TL, 144 mm DW, between Paranaguá, Paraná and Ilha do Bom Abrigo, São Paulo. DBAV.UERJ 1623.1, male, 210 mm TL, 120 mm DW, DBAV.UERJ 1623.2, male, 225 mm TL, 138 mm DW, Santos. DBAV.UERJ 1627.4, female, 267 mm TL, 135 mm DW, Santos. DBAV.UERJ 1720.1, female, 242 mm TL, 135 mm DW, DBAV.UERJ 1720.2, male, 185 mm TL, 106 mm DW, DBAV.UERJ 1720.3, female, 178 mm TL, 87 mm DW, DBAV.UERJ 1720.5, female, 154 mm TL, 82 mm DW, DBAV.UERJ 1720.6, female, 235 mm TL, 133 mm DW, Arquipélago de Alcatrazes. DBAV.UERJ 1868, male, 220 mm TL, 118 mm DW, Santos. DBAV.UERJ 1871.1, male, 84 mm TL, 44 mm DW, DBAV.UERJ 1871.2, female, 272 mm TL, 148 mm DW, between Paranaguá, Paraná and Ilha do Bom Abrigo, São Paulo. DBAV.UERJ 1874.3, male, 255 mm TL, 135 mm DW, DBAV.UERJ 1874.4, male, 251 mm TL, 140 mm DW, Ubatuba. DBAV.UERJ 1885.9*, female, 200 mm TL, 115 mm DW, Barra de Santos. DBAV.UERJ 1886.1, female, 195 mm TL, 110 mm DW, Barra de Santos. DBAV.UERJ 1886.8, male, 202 mm TL, 120 mm DW, Barra de Santos. Rio de Janeiro: DBAV.UERJ 759, female, 176 mm TL, 100 mm DW, Maricá. DBAV.UERJ 763, female, 176 mm TL, 100 mm DW, Ilha Grande. DBAV.UERJ 2124, female, 263 mm TL, 145 mm DW, DBAV.UERJ 2125, female, 261 mm TL, 138 mm DW, DBAV.UERJ 2126, female, 247 mm TL, 138 mm DW, DBAV.UERJ 2127, male, 258 mm TL, 140 mm DW, DBAV.UERJ 2128, female, 231 mm TL, 134 mm DW, DBAV.UERJ 2129, female, 206 mm TL, 115 mm DW,DBAV.UERJ 2139, female, 262 mm TL, 135 mm DW,Angra dos Reis. DBAV.UERJ 2144.2*, female, 275 mm TL, 165 mm DW, 23º27.4’S 44º13.4’W. DBAV.UERJ 2146.8, female, 240 mm TL, 149 mm DW, Angra dos Reis. MNRJ 14159, male, 254 mm TL, 141 mm DW, Ilha Feia. MNRJ 17763, 2, 246–253 mm TL, 143–153 mm DW, Macaé. MNRJ 32323, 5, 125.8–267 mm TL, 77–152 mm DW, Rio de Janeiro. MNRJ 32468, 3, 233–262 mm TL, 129.85–141.5 mm DW, Rio de Janeiro. MNRJ 32595, 2, 107.95–141.9 mm TL, 61.85–77.65 mm DW, Rio de Janeiro. MNRJ 33103, 3, 225–245 mm TL, 129–140 mm DW, between Ilha Rasa and Marambaia. MNRJ 49365, male, 235 mm TL, 115 mm DW, Armação dos Búzios. MNRJ 49227, male, 245 mm TL, 131.5 mm DW, Armação dos Búzios. Locality undetermined: DBAV.UERJ 1645, male, 245 mm TL, 137 mm DW. DBAV.UERJ uncataloged*, male, 262 mm TL, 144.7 mm DW.

Psammobatis lentiginosa McEachran, 1983

Psammobatis extenta —Norman, 1937:28 (in part) (Patagonia; catalogue).

Psammobatis lentiginosa McEachran, 1983:62, fig. 17 (original description; type-locality: off the coast of Uruguay). —Andreata, Séret, 1995:581 (Espírito Santo, Brazil; listed). —McEachran, Dunn, 1998 (systematic study). —Compagno, 1999:489 (listed). —Mazzoleni, Schwingel, 1999:114 (Itajaí, Santa Catarina, Brazil; listed). —Cousseau et al., 2000:29 (Argentina and Uruguay; catalogue). —Menni, Stehmann, 2000:87 (Argentina, Uruguay and Brazil; listed). —Paragó, 2001 (systematic study). —Gomes, 2002 (systematic study). —Gomes, Gadig, 2003:29 (São Paulo, Brazil; listed). —Mabragaña, 2007 (Argentina; biological and ecological study). —Cousseau et al., 2007:64 (Mar del Plata, Argentina; catalogue). —Perier et al., 2011 (Argentina; reproductive biology). —Mabragaña et al. 2012 (reproductive biology). —Weigmann, 2016:100 (listed). —Last et al., 2016:458 (listed). —Nión et al., 2016:23 (Uruguay; listed). —Gomes et al., 2019:300, fig. 292 (Rio de Janeiro, Brazil; catalogue). —Brum-Neto, Lucena, 2020 (Brazil; tooth morphology). —Mabragaña et al., 2020 (systematic study). —Sabadin et al., 2020:1900–1 (Argentina, Uruguay and Brazil; listed). —Mabragaña, Cousseau, 2021:65 (Argentina; listed). —Gabbanelli et al., 2022 (systematic and biological study).

Diagnosis. Psammobatis lentiginosa is distinguished from P. extenta and P. rutrum by the dark brown background color with darker spots distributed randomly throughout the dorsal region (vs. smaller spots in P. extenta and whitish spots in P. rutrum); thorns on the pectoral fin reduced or absent (vs. present in P. extenta and P. rutrum); interruption of only the middorsal thorn row up to the axillary region of pelvic fin (vs. continuous dorsal thorns rows after the scapular region in P. extenta and interruption of all three rows in P. rutrum); a rough band of denticles in dorsal central region, contrasting with the smooth aspect of pectoral fins (vs. absence of contrast in P. extenta and P. rutrum); thorns reduced or absent in the pectoral posterior region of males (vs. present in P. extenta and P. rutrum); females with well-developed prickles on the posterior lobe of the pelvic fins (vs. dermal denticles poorly developed in P. extenta and P. rutrum); anterior fontanelle trapezoidal (vs. rectangular in P. extenta); basal fenestrae kidney-shaped (vs. rectangular and narrow in P. extenta); dorsal terminal cartilage 2 plate-shaped (vs. triangular in P. rutrum and absent P. extenta); accessory terminal cartilage 2 projected transversely to lateral (vs. flattened dorsoventrally in P. rutrum and absent in P. extenta); accessory terminal cartilage 1 articulated with the ventral marginal cartilage (vs. continuous in P. extenta).

External description. Disc 1.6–1.8 times wider than long (Tab. 3). Heart-shaped disc in juvenile and adult specimens; subtle in the former and accentuated in the latter. Adults with wide pectoral fins and convex margins in the posterior region, while the anterior region narrows towards the snout. Adult males with concave anterior disc margin close to the orbital region; disc width at eye line in females is 1.1 times longer than in males.

TABLE 3 | Morphometric measurements for males and females of Psammobatis lentiginosa. Disc width (DW) in millimeters and other measurements as percentages of disc width (% DW). CL, caudal length; DGS1, distance between first gill slits; DGS5, distance between fifth gill slits; DL, disc length; DWE, disc width at eye line; EYD, eye diameter; FDC, distance from first dorsal fin origin to posterior end of caudal fin; GS1, first gill slit width; GS3, third gill slit width; GS5, fifth gill slit width; INO, interorbital distance; INW, internasal distance; MOW, mouth width; PFD, distance from posterior margin of pelvic fin to first dorsal fin origin; PNR, prenasal length; POB, preorbital length; POR, preoral length; SVL, snout-vent length; TL, total length.

Measurements	Females			Males
	Mean	Range	N	Mean	Range	N
TL	186.9	172.6–194.8	14	189.0	183.0–197.3	8
DW	141.4	61.3–185.0	14	153.8	104.0–215.0	8
CL	107.7	100.5–115.1	14	110.6	103.0–117.3	8
DL	86.9	81.0–92.5	14	85.0	81.9–87.9	8
POB	21.7	18.3–25.7	14	19.0	16.4–22.8	8
PNR	17.1	15.4–19.2	14	14.1	11.9–19.0	8
INW	8.7	7.3–9.6	14	8.5	7.6–9.7	8
EYD	6.8	5.9–7.9	14	6.5	5.7–7.5	8
INO	6.6	5.24–7.7	14	6.4	5.9–6.7	8
POR	24.3	22.0–28.5	14	20.0	16.9–23.8	8
SVL	80.7	78.6–83.6	14	78.7	74.4–81.4	8
MOW	14.3	12.3–16.3	14	14.7	11.5–17.9	8
FDC	23.3	20.1–30.0	13	22.3	18.7–28.6	8
PFD	63.9	58.4–72.4	14	64.5	58.4–70.9	8
GS1	3.2	2.6–3.7	13	3.4	3.0–4.3	8
GS3	3.0	2.4–3.4	13	3.1	2.9–3.4	8
GS5	2.4	1.9–3.0	13	2.2	1.9–2.5	8
DGS1	24.6	22.9–26.9	14	24.1	22.4–25.9	8
DGS5	13.5	12.1–16.3	14	11.5	10.7–12.5	8
DWE	62.7	55.3–75.5	14	55.0	49.9–63.6	8

Preorbital length 2.9–3.2 times eye horizontal diameter and 3.0–3.3 times interorbital distance. Preoral length 1.4–1.7 times mouth width. Upper jaw arched, especially in middle region; lower jaw convex. First pair of gill openings 1.3–1.5 times larger than fifth. Distance between first gill slits 1.8–2.1 times the distance between fifth.

Pelvic fins convex externally with a notch forming anterior and posterior lobes. Pelvic anterior lobe shorter with convex anterior margin; posterior margin distinguished by radial tips and continuously connected to lateral margin of posterior lobe. Posterior lobe with a convex lateral margin and a straight inner margin. Dorsal fins similar in size and shape, with rounded apex. Distance from the pelvic posterior margin to origin of first dorsal fin 2.7–2.9 times the distance from first dorsal origin to posterior margin of caudal fin. Tail long, 1.7 times in total length and 1.3–1.4 times the snout-vent distance. Caudal fin rounded.

Coloration in alcohol. Dorsal coloration dark brown, covered with darker spots distributed randomly and sometimes forming circles (Fig. 3C). Whitish spots distributed over the dorsal surface. Preorbital region with a lighter triangular area contrasting to the predominant background color as in P. extenta (Figs. 3A, C). In juveniles, a dark spot located in the central region of each pectoral fin as in P. rutrum (Figs. 3E, 5B). Black spot on the snout tip present in some specimens as in P. extenta and P. rutrum (Figs. 3A, C, E). Tail region similar to that described for the rest of the body. Ventral region predominantly cream (Fig. 3D).

Dermal denticles. Rostral and malar thorns forming rows with no differences between sexes; star-shaped base and a curved crown that narrows towards its distal end (Fig. 10E). Rows of alar thorns of adult males situated posterior to the malars and positioned horizontally, close to pectoral lateral margin, with distal end oriented medially; elongated base and a thorn-shaped crown, arranged in one to three alternating rows, with around five to 20 denticles (Fig. 10A; Tab. 2).

FIGURE 10| Dermal denticles of Psammobatis lentiginosa from specimens DBAV.UERJ 86551, adult male, 315 mm TL (A, B, C) and MZUSP 86758, immature female, 226 mm TL (D, E, F). A. Alar thorns. B. Posterior-pectoral thorns (male). C. Scapular thorns. D. Posterior-pectoral thorns (female). E. Rostral thorns. F. Pelvic dermal denticles (prickles). Scale bars = 200 µm. Anter, anterior region; Post, posterior region.

Head with one to four preorbital thorns, none to two midorbital thorns, none to two postorbital thorns, and none to four spiracular thorns. Thorns similar in structure to the nuchal and scapular. Nuchal and scapular thorns fworming a triangular grouping, organized into one to three nuchal thorns and three to 16 scapular thorns; leaf-shaped base with shallow grooves and a curved crown with an extremely sharp distal end (Fig. 10C).

No mid-pectoral thorns on pectoral fins. Thorns reduced or absent on pectoral fins of adults, giving a smooth appearance. Posterior pectoral thorns present in females and reduced or absent in adults males; cross-shaped or star-shaped base, with a curved crown and tapered distal end (Figs. 10B, D).

Males with no dermal denticles on their claspers (Fig. 8B). Adult females with a cluster of prickles located on the posterior lobe of the pelvic fin; cross-shaped base and crown curved with a tapered distal end (Fig. 10F). Adult males with reduced or absent dermal denticles on this region.

Middorsal row of thorns presenting an interruption that extends to pelvic insertion. Middorsal and dorsolateral thorns similar in structure to nuchal and scapular thorns but relatively smaller. Smaller denticles present posteriorly to scapula and around rows, giving a rough texture to this region (Fig. 4E). Cross-shaped base and crown curved with a tapered distal end.

One row of mid-caudal thorns and two caudo-lateral thorns, one on each side of the tail, all oriented anterior-posteriorly. Caudo-lateral thorns with base and crown flattened dorsolaterally. Mid-caudal thorns similar in structure to the middorsal thorns and forming a continuous row with them, with around 26 to 54 denticles (Tab. 2).

Geographical distribution. Examined specimens collected between Rio de Janeiro and Santa Catarina; most of the collection sites are concentrated in Santa Catarina (Fig. 9). The geographic distribution of P. lentiginosa extends as far as the Gulf of San Jorge, Argentina (Mabragaña, 2007).

Material examined. BMNH 1935.9.11.2, holotype. ZMH 25230 [ex ISH 1034–1966], 1. ZMH 25231 [ex 1501–1966], 1. ZMH 25232 [ex 1622–1966], 1. ZMH 25233 [ex 1676–1966], 1. MZUSP 13089–102, 14, paratypes, off the coast of Uruguay, 34°S 50°W. Santa Catarina: MZUSP 42847, male, 312 mm TL, 166 mm DW, between Rio de Janeiro and Santa Catarina. MZUSP 86551*, male, 315 mm TL, 171 mm DW, 26°42’7.0”S 46°43’19.0”W. MZUSP 86758*, female, 226 mm TL, 126 mm DW, between Rio de Janeiro and Santa Catarina. MZUSP 127757, 4, 280–406 mm TL, 146–215 mm DW. MZUSP 127758, 6, 283–345 mm TL, 153–185 mm DW, Bombinhas. MZUSP 127759, 8, 118.4–306 mm TL, 61.3–162 mm DW, Bombinhas. Locality undetermined: MNRJ 20608, 2, 290–296 mm TL, 150–150 mm DW.

Psammobatis rutrumJordan, 1891

Psammobatis rutrum Jordan, 1891:334 (original description; type-locality: near Gulf San Matías, Argentina). —McEachran, 1983:58, fig. 16c (systematic study). — McEachran, Dunn, 1998:286 (systematic study). —Compagno, 1999:489 (listed). —Cousseau et al., 2000:31 (Argentina and Uruguay; catalogue). —Menni, Stehmann, 2000:87 (Argentina, Uruguay and Brazil; listed). —Paragó, 2001 (systematic study). —Gomes, 2002 (systematic study). —Gomes, Gadig, 2003:29 (São Paulo, Brazil; listed). —Mabragaña, 2007 (Argentina; biological and ecological study). —Cousseau et al., 2007:70 (Mar del Plata; Argentina; catalogue). —Weigmann, 2016:100 (listed). —Last et al., 2016:461 (listed). —Nión et al., 2016:23 (Uruguay; listed). —Martins, Oddone, 2017 (Brazil; reproductive biology). —Viana et al., 2017:3 (Rio de Janeiro, Brazil; diet). —Cordeiro, Oddone, 2019:47 (Rio Grande do Sul, Brazil; reproductive biology). —Gomes et al., 2019:301, fig. 293 (Rio de Janeiro, Brazil; catalogue). —Brum-Neto, Lucena, 2020 (Brazil; tooth morphology). Sabadin et al., 2020:1900–1 (Argentina, Uruguay and Brazil; listed). —Batista et al., 2021 (Barra de Santos, São Paulo, Brazil; reproductive biology). —Mabragaña, Cousseau, 2021:65 (Argentina; listed).

Raia extenta —Garman, 1913:356 (systematic account).

Malacorhina cirrifer —Regan, 1914:16 (systematic account).

Psammobatis extenta —Figueiredo, 1977:33, fig. 74 (Southern Brazil; catalogue).

Diagnosis. Psammobatis rutrum is distinguished from P. extenta and P. lentiginosa by the brown coloration pattern with whitish spots distributed randomly throughout dorsal region (vs. tiny dark dots in P. extenta and dark dots in P. lentiginosa);dark dot on the central of pectoral fins in adults and juveniles (vs. absent in adults in P. extenta and P. lentiginosa); tiny spots concentrated in preorbital region (vs. distributed around orbits P. extenta and absent in P. lentiginosa); pectoral thorns with tip oriented towards lateral margin of disc (vs. tip oriented towards caudal region in P. extenta and reduced or absent in P. lentiginosa); interruption of the three rows of dorsal thorns posterior to scapular region (vs. continuous rows of dorsal thorns in P. extenta and interruption only from the middorsal to pelvic insertion in P. lentiginosa); anterior fontanelle trapezoidal (vs. rectangular in P. extenta); basal fenestrae kidney-shaped (vs. rectangular and narrow in P. extenta); posterior nasal cartilage oblique in relation the anteroposterior axis (vs. perpendicular in relation the anteroposterior axis in P. extenta); dorsal terminal cartilage 2 triangular (vs. plate-shaped in P. lentiginosa and absent P. extenta); accessory terminal cartilage 2 flattened dorsoventrally (vs. projected transversely to lateral in P. lentiginosa and absent in P. extenta); accessory terminal cartilage 1 articulated with the ventral marginal cartilage (vs. continuous in P. extenta).

External description. Disc 1.5–1.7 times wider than long (Tab. 4). Heart-shaped disc in juvenile and adult specimens; subtle in the former and accentuated in the latter. Adults with wide pectoral fins and convex margins in the posterior region, while the anterior region narrows towards the snout. Adult males with concave anterior disc margin close to the orbital region; disc width at eye line in females is 1.2 times longer than in males.

TABLE 4 | Morphometric measurements for males and females of Psammobatis rutrum. Disc width (DW) in millimeters and other measurements as percentages of disc width (% DW). CL, caudal length; DGS1, distance between first gill slits; DGS5, distance between fifth gill slits; DL, disc length; DWE, disc width at eye line; EYD, eye diameter; FDC, distance from first dorsal fin origin to posterior end of caudal fin; GS1, first gill slit width; GS3, third gill slit width; GS5, fifth gill slit width; INO, interorbital distance; INW, internasal distance; MOW, mouth width; PFD, distance from posterior margin of pelvic fin to first dorsal fin origin; PNR, prenasal length; POB, preorbital length; POR, preoral length; SVL, snout-vent length; TL, total length.

Measurements	Females			Males
	Mean	Range	N	Mean	Range	N
TL	171.4	159.6–183.0	14	180.5	156.2–219.7	9
DW	140.2	75.3–166.0	14	126.9	110.2–140.0	9
CL	90.9	78.1–101.5	14	100.8	80.8–129.8	9
DL	82.9	74.9–90.3	14	87.3	77.8–99.0	9
POB	17.1	12.1–22.6	14	16.8	13.6–20.8	8
PNR	13.9	12.0–18.7	14	11.9	10.5–15.1	8
INW	7.3	4.5–8.4	14	7.5	6.6–8.8	9
EYD	5.3	4.0–6.6	14	6.6	4.9–8.9	9
INO	6.7	5.8–7.7	14	6.6	5.8–7.3	9
POR	20.0	16.8–26.6	14	17.4	14.7–19.9	9
SVL	75.7	70.2–81.7	14	76.2	68.6–83.9	8
MOW	11.6	10.2–16.1	14	13.9	11.6–20.0	9
FDC	23.9	15.2–28.0	13	28.5	19.9–33.6	6
PFD	50.7	42.7–56.9	13	54.7	43.3–75.2	6
GS1	3.5	2.5–4.4	13	3.5	2.7–4.2	9
GS3	3.2	2.5–4.0	13	3.3	2.6–4.2	9
GS5	2.7	2.2–3.5	13	2.6	2.1–3.4	9
DGS1	24.5	22.2–26.8	11	22.9	17.3–26.7	9
DGS5	13.4	11.6–14.8	11	11.8	10.9–13.7	8
DWE	61.0	54.8–75.7	14	50.1	45.7–55.9	9

Preorbital length 2.5–3.2 times eye horizontal diameter and 2.5–2.6 times interorbital distance. Preoral length 1.3–1.7 times mouth width. Upper jaw arched, especially in middle region; lower jaw convex. First pair of gill openings 1.3 times larger than fifth. Distance between the first gill slits 1.8–1.9 times the distance between fifth.

Pelvic fins convex externally with a notch forming anterior and posterior lobes. Pelvic anterior lobe shorter with a convex anterior margin; posterior margin distinguished by radial tips and continuously connected to the lateral margin of posterior lobe. Posterior lobe with a convex lateral margin and a straight inner margin. Dorsal fins similar in size and shape, with rounded apex. Distance from pelvic posterior margin to the origin of first dorsal fin 1.9–2.1 times distance from first dorsal origin to posterior margin of caudal fin. Tail long, 1.8–1.9 times in total length and 1.2–1.3 times the snout-vent distance. Caudal fin rounded.

Coloration in alcohol. Dorsal coloration brown (Fig. 3E). Adults with whitish spots all over the dorsal surface. Dark spot in the central region of each pectoral fin and another in each region of malar thorns in both adults and juveniles (Figs. 3E, 5C). A cluster of dark spots located on posterior region of each pectoral fin (may not be visible in juveniles). Preorbital region with tiny dark spots, projecting towards disc margin (Fig. 4C). Some specimens present a black spot on snout tip as in P. extenta and P. lentiginosa. Tail region presenting the same predominant background color. Ventral region uniformly cream (Fig. 3F).

Dermal denticles. Rostral and malar thorns forming rows with no differences between sexes; star-shaped base and a curved crown that narrows towards its distal end (Figs. 11C–D). Adult males with rows of alar thorns situated posterior to the malars and positioned horizontally, close to the pectoral lateral margin, with the distal end oriented medially; elongated base and a thorn-shaped crown, arranged in one to three alternating rows, with around five to 20 denticles (Fig. 11A; Tab. 2).

FIGURE 11| Dermal denticles of Psammobatis rutrum from specimen DBAV.UERJ 2130, adult male, 251 mm TL. A. Alar thorns. B. Posterior-pectoral thorns. C. Malar thorns. D. Rostral thorns. E. Nuchal thorns. F. Scapular thorns. Scale bars = 200 µm. Anter, anterior region; Post, posterior region.

Head with one to five preorbital thorns, one to three midorbital thorns, none to two postorbital thorns, and one to four spiracular thorns. Thorns similar in structure to the nuchal and scapular but smaller. Nuchal and scapular thorns forming a triangular grouping, organized into one to three nuchal thorns and five to 17 scapular thorns. Scapular thorns more dispersed, resulting in an arch in some individuals; leaf-shaped base with shallow grooves and a curved crown with an extremely sharp distal end (Figs. 11E–F).

No mid-pectoral thorns on pectoral fins. Pectoral thorns scattered randomly throughout the pectoral fin and varying in size; stellate base poorly defined and tip slightly inclined to posterior margin of pectoral fin (Figs. 7C–D). Posterior pectoral thorns present in both males and females. Larger and more clustered; cross-shaped or star-shaped base, with a curved crown and tapered distal end. Males lack dermal denticles on their claspers (Fig. 9C).

Middorsal and dorsolateral thorns with an interruption after between scapula and pelvic insertion (Fig. 11F). Middorsal and dorsolateral thorns similar in structure to nuchal and scapular thorns. Smaller denticles present posteriorly to scapula and around rows. Cross-shaped base and crown curved with a tapered distal end.

One row of mid-caudal thorns and two caudo-lateral thorns, one on each side of tail, all oriented anteroposteriorly; denticles arranged randomly between rows. Caudo-lateral thorns with base and crown flattened dorsolaterally. Mid-caudal thorns similar in structure to middorsal thorns and forming a continuous row with them, with around 15 to 34 denticles (Tab. 2).

Geographical distribution. Although some specimens do not have the capture locality, the distribution is also between the coasts of Rio de Janeiro, São Paulo, and, mainly, Rio Grande do Sul (Fig. 9). Records of P. rutrum are also found in northern Argentina (Cousseau et al., 2007).

Material examined. USNM 43431, holotype, near Gulf San Matías, off the coast of Argentina, Albatross Station 2678, 42°00’24”S 61°38’30”W, depth 78 meters. São Paulo: DBAV.UERJ 848.3*, female, 230 mm TL, 140 mm DW, Santos. Rio de Janeiro: DBAV.UERJ 2142.8*, female, 251 mm TL, 144 mm DW, Angra dos Reis. MNRJ 607, 3, 242–264 mm TL, 110.15–160 mm DW, Ilha Rasa. MNRJ 32626, female, 263 mm TL, 151 mm DW, Rio de Janeiro. MNRJ 33565, 3, 247–265 mm TL, 133–166 mm DW, between Ilha Rasa and Marambaia. Rio Grande do Sul: MNRJ 20610, 2, 203–245 mm TL, 130–142 mm DW. MZUSP 9953, male, 235 mm TL, 134 mm DW. MZUSP 9954, female, 242 mm TL, 140 mm DW. MZUSP 13128, female, 231 mm TL, 142 mm DW. MZUSP 13129, female, 242 mm TL, 143 mm DW, 31°19’0.0”S 50°22’0.0”W. MZUSP 45151, 2, 125.4–257 mm TL, 75.3–147 mm DW, 31°48’0.0”S 50°22’0.0”W. MZUSP 45152*, male, 240 mm TL, 140 mm DW, 31°50’0.0”S 50°21’0.0”W. Locality undetermined: DBAV.UERJ 2130*, male, 251 mm TL, 137 mm DW. AC.DBAV.UERJ 937.1, male, 215 mm TL, 125 mm DW. MNRJ 20609, 2, 194–222 mm TL, 115.35–117.4 mm DW.

Statistical analysis. Significant differences between males and females were observed in six measurements within P. extenta, five in P. lentiginosa and seven in P. rutrum (Tab. S1). In P. extenta, measurements with significant p-values (< 0.05) were prenasal length (T: 2.577, df = 35, p = 0.014), eye diameter (T: -3.156, df = 28, p = 0.004), preoral length (T: 2.4161, df = 31, p = 0.021), mouth width (T: -2.1475, df = 35, p = 0.039), distance between fifth gill slits (W: 191, p = 0.001) and disc width at eye line (T: 4.4696, df = 35, p = 0.000). For P. lentiginosa, the significantly different measures were preorbital length (T: 2.8283, df = 20, p = 0.010), prenasal length (W: 93, p = 0.010), preoral length (T: 5.7438, df = 20, p = 0.000), distance between fifth gill slits (T: 3.7949, df = 20, p = 0.001) and disc width at eye line (T: 4.3859, df = 20, p = 0.000). In P. rutrum, significant differences were observed in prenasal length (T: 3.6525, df = 20, p = 0.002), eye diameter (T: -2.4898, df = 21, p = 0.021), preoral length (W: 116, p = 0.000), mouth width (W: 29, p = 0.033), distance between first gill slits (T: 3.4305, df = 18, p = 0.003), distance between fifth gill slits (T: 5.4503, df = 14, p = 0.000) and disc width at eye line (T: 6.9238, df = 21, p = 0.000).

Analyses between species resulted in seventeen measurements with p-values lower than 0.05, in the Kruskal-Wallis test (Tab. S2). Using Dunn’s test, differences between species were identified for each variable analyzed (Tab. S3). Differences between P. extenta and P. lentiginosa were observed for caudal length (p = 0.000), disc length (p = 0.012), preorbital length (p = 0.000), prenasal length (p = 0.000), internasal distance (p = 0.000), eye diameter (p = 0.000), preoral length (p = 0.000), snout-vent length (p = 0.000), mouth width (p = 0.000), distance from first dorsal fin origin to posterior end of caudal fin (p = 0.001). For P. rutrum and P. extenta, significant variables were disc width (p = 0.005), disc length (p = 0.001), internasal distance (p = 0.046), eye diameter (p = 0.028), snout-vent length (p = 0.000) and distance between fifth gill slits (p = 0.044). For P. lentiginosa and P. rutrum, significant values were obtained for the variables disc width (p = 0.048), caudal length (p = 0.000), preorbital length (p = 0.001), prenasal length (p = 0.008), internasal distance (p = 0.023), interorbital distance (p = 0.042), preoral length (p = 0.005), mouth width (p = 0.007), distance from first dorsal fin origin to posterior end of caudal fin (p = 0.000), distance from posterior margin of pelvic fin to first dorsal fin origin (p = 0.000), first gill slit width (p = 0.019) and fifth gill slit width (p = 0.004).

Comparative morphology of internal structures.

Neurocranium. The neurocranium of the three Psammobatis species is compressed dorsoventrally and has an hourglass shape, with the greatest width located in the medial section of the nasal capsules and the second greatest in the section of the otic capsules (Figs. 12–14). Rostrum not observed, but it is very thin and uncalcified, not continuous or fused to the neurocranium (McEachran, 1983).

FIGURE 12| Neurocranium of Psammobatis extenta, MNRJ 32468, female, 370 mm TL. A. Dorsal view, B. Ventral view, C. Lateral view. II, foramen for the optic nerve; III, foramen for the oculomotor nerve; IV, foramen for the trochlear nerve; VI, foramen for the abducens nerve; acvf, anterior canal vein foramen; af, anterior fontanelle; antf, antorbital facet; apba, foramen for the afferent pseudobranchial artery; bf, basal fenestra; bp, basal plate; end, endolymphatic foramen; epb, epiphysial bridge; fm, foramen magnum; hf, hyomandibular facet; hVII, foramen for the passage of the hyomandibular ramus of the facialis nerve; icf, internal carotid artery foramen; inc, inner nasal cartilage; ja, jugal arch; na, nasal aperture; nc, nasal capsule; oc, otic capsule; occ, occipital condyle; onc, outer nasal cartilage; opf, ophthalmic foramen; ornc oronasal canal; peri, perilymphatic foramen; pf, posterior fontanelle; pnc, posterior nasal cartilage; pos, postorbital process; pre, preorbital process; prof, prootic foramen; ptp, pterotic process; sopf, superficial ophthalmic foramina. Scale bar = 10 mm.

FIGURE 13| Neurocranium of Psammobatis lentiginosa, MZUSP 127759, male, 306 mm TL. A. Dorsal view, B. Ventral view. af, anterior fontanelle; bp, basal plate; end, endolymphatic foramen; epb, epiphysial bridge; icf, internal carotid artery foramen; ja, jugal arch; nc, nasal capsule; oc, otic capsule; occ, occipital condyle; peri, perilymphatic foramen; pf, posterior fontanelle; pos, postorbital process; pre, preorbital process; ptp, pterotic process. Scale bar = 10 mm.

FIGURE 14| Neurocranium of Psammobatis rutrum, MZUSP 9953, male, 235 mm TL. A. Dorsal view, B. Ventral view. af, anterior fontanelle; bf, basal fenestra; bp, basal plate; end, endolymphatic foramen; epb, epiphysial bridge; icf, internal carotid artery foramen; inc, inner nasal cartilage; ja, jugal arch; na, nasal aperture; nc, nasal capsule; nf, nasal fontanelle; oc, otic capsule; occ, occipital condyle; onc, outer nasal cartilage; peri, perilymphatic foramen; pf, posterior fontanelle; pnc, posterior nasal cartilage; pos, postorbital process; pre, preorbital process; ptp, pterotic process. Scale bar = 10 mm.

Nasal capsule slightly oblique in relation to the anteroposterior axis, with thin walls and a basal fenestra, located in the anterodorsal region, varying from kidney-shaped in P. rutrum and P. lentiginosa to rectangular and narrow in P. extenta (Figs. 12–16). Nasal aperture relatively narrow, 1.4–1.5 times in the internasal distance (Tab. 5). Antorbital facet lies on the lateral surface of the nasal capsule, close to its posterior margin, and articulating to the antorbital cartilage. Nasal cartilages not preserved in P. lentiginosa. In P. extenta and P. rutrum, outer nasal cartilage triangular and short, not dividing incurrent and excurrent apertures (Fig. 16). Internal nasal cartilage rectangular in shape and running laterally from the nasal fontanelle, adjacent to the internasal septum, dorsal and attached to the posterior nasal cartilage medially. Posterior nasal cartilage narrow at the anterior tip, wide and rounded at the posterior tip and perpendicular in relation the anteroposterior axis in P. extenta, while uniformly wide and oblique in relation the anteroposterior axis in P. rutrum (Fig. 16).

FIGURE 15| Neurocranium of Psammobatis species, dorsal view. A. P. extenta, MNRJ 32468, female, 370 mm TL. B. P. lentiginosa, MZUSP 127759, male, 306 mm TL. C. P. rutrum, MZUSP 9953, male, 235 mm TL. af, anterior fontanelle; bf, basal fenestra; end, endolymphatic foramen; epb, epiphysial bridge; ja, jugal arch; nc, nasal capsule; peri, perilymphatic foramen; pf, posterior fontanelle; pos, postorbital process; pre, preorbital process; prf, parietal fossa; ptp, pterotic process.

TABLE 5 | Neurocranial measurements in percentages of nasobasal length (% NL) of specimens of Psammobatis extenta, P. rutrum and P. lentiginosa.

Measurements	P. extenta (MNRJ 32468)	P. lentiginosa (MZUSP 127759)	P. rutrum (MZUSP 9953)
Width across nasal capsules	91.80	79.68	81.40
Nasal aperture width	13.77	–	14.25
Internasal distance	20.96	18.97	20.98
Interorbital distance	29.49	26.24	27.54
Anterior fontanelle length	34.10	27.69	23.80
Anterior fontanelle width	21.82	15.20	11.04
Epiphyseal bridge width	6.53	5.66	3.35
Posterior fontanelle length	48.72	46.69	46.53
Posterior fontanelle width	11.32	10.25	14.86
Basal plate width	27.70	25.13	26.08
Width across otic capsules	58.55	50.66	47.17
Neurocranium length	110.39	106.92	109.51

FIGURE 16| Neurocranium of Psammobatis species, ventral view. A. P. extenta, MNRJ 32468, female, 370 mm TL. B. P. lentiginosa, MZUSP 127759, male, 306 mm TL. C. P. rutrum, MZUSP 9953, male, 235 mm TL. bp, basal plate; icf, internal carotid artery foramen; inc, inner nasal cartilage; ins, internasal space; na, nasal aperture; nf, nasal fontanelle; oc, otic capsule; occ, occipital condyle; onc, outer nasal cartilage; oop, olfactory opening; pnc, posterior nasal cartilage.

Cranial roof extends from the posterior margin of the anterior fontanelle to the parietal fossa. Anterior fontanelle rectangular in P. extenta and trapezoidal in P. rutrum and P. lentiginosa (Figs. 12–15), limited anteriorly by the anterior cranial margin, extending to the anterior edge of the supraorbital ridge. Epiphyseal bridge thin, equivalent to 4.9–7.1 times the length of the anterior fontanelle (Tab. 5). Posterior fontanelle sub-rectangular, 1.6–1.7 times longer than the anterior fontanelle (Tab. 5). Posterior margin moderately pointed in P. lentiginosa while slightly pointed in P. extenta and P. rutrum (Fig. 15). Preorbital process continuous with the supraorbital ridge and relatively developed in P. extenta and P. rutrum, while it is less noticeable in P. lentiginosa (Fig. 15).

Orbital region delineated anteriorly by the posterior wall of the nasal capsules and posteriorly by the anterior margin of the otic capsules, dorsally delimited by the cranial roof and ventrally by the basal plate (Fig. 17). Orbital wall perforated by several foramina for the passage of cranial nerves and blood vessels. Oronasal canal lies anteriorly and near the posterior wall of nasal capsules. Foramina for the anterior cerebral vein situated posterior to the oronasal canal. Foramina for the ophthalmicus nerve situated dorsally near the supraorbital crest. Posterior to the foramen for the optic nerve (II) and dorsal to the optic nerve foramen, there is a single foramen for the trochlear nerve (IV). The foramen for the optic nerve lies anteriorly to the half-length of orbital wall, quite near the foramina for the anterior cerebral vein in P. rutrum than in P. extenta and P. lentiginosa (Fig. 17). Posterior to the foramen for the trochlear nerve is the foramen for the oculomotor nerve (III), posterior to half-length of orbital wall. The foramen for the afferent pseudobranchial artery is located ventrally to the foramen for the oculomotor nerve, close to the basal plate. Dorsally, on the same vertical line as the foramen for the afferent pseudobranchial artery, is the foramen for the abducens nerve (VI) in P. lentiginosa and P. extenta, while in P. rutrum it is located posteriorly on the same horizontal line. Anterior to the otic region, the foramina for superficial ophthalmic is located in dorsal portion, the foramen prootic in medial portion and the foramen for the passage of the hyomandibular ramus of the facialis nerve (hVII), in ventral portion (Fig. 17).

FIGURE 17| Neurocranium of Psammobatis species, lateral view. A. P. extenta, MNRJ 32468, female, 370 mm TL. B. P. lentiginosa, MZUSP 127759, male, 306 mm TL. C. P. rutrum, MZUSP 9953, 235 mm TL, male, Rio Grande do Sul, RS. II, foramen for the optic nerve; III, foramen for the oculomotor nerve; IV, foramen for the trochlear nerve; VI, foramen for the abducens nerve; acvf, anterior canal vein foramen; antf, antorbital facet; apba, foramen for the afferent pseudobranchial artery; hf, hyomandibular facet; hVII, foramen for the passage of the hyomandibular ramus of the facialis nerve; opf, ophthalmic foramen; ornc, oronasal canal; pnc, posterior nasal cartilage; prof, prootic formamen; sopf, superficial ophthalmic foramina.

Basal plate begins anteriorly at the ethmoidal fossa right after the nasal capsules, runs to the posteroventral end of the optic region and ends at the ventral margin of the foramen magnum. A single foramen for the internal carotid artery ventrally situated and slightly anterior to the level of the postorbital process (Fig. 16).

Otic region begins posterior to orbital wall and extends to occipital region, containing otic capsules, impressions of semicircular canals and parietal fossa. Parietal fossa lies posteriorly and between otic capsules, with a pair of endolymphatic canals (smaller apertures) and another pair of perilymphatic canals (Fig. 16). Hyomandibular facet elongated and positioned obliquely on the lateral otic region, lined dorsally by the postorbital groove and jugal arch (Fig. 17).

Occipital condyle situated on the lateral margin of the foramen magnum and lateral to it lies the foramen for the vagus nerve (X). Lateral to the foramen for the vagus nerve lies the foramen for the glossopharyngeal nerve (IX).

Clasper. The clasper of the three Psammobatis species is slender and covered entirely by the dorsal and ventral lobes of glans. External morphology varies mainly in terms of the coverage of dermal denticles and the position of the spermatic groove. Dermal denticles present along the margins of spermatic groove in P. extenta and absent in P. rutrum and P. lentiginosa. Spermatic groove and hypopyle located entirely in lateral position in P. rutrum and P. lentiginosa, while found in dorsal position in P. extenta (Figs. 8, 18).

FIGURE 18| External morphology of the right clasper of Psammobatis species; dorsal view. A. P. extenta, DBAV.UERJ uncatalogued, 262 mm TL. B. P. lentiginosa, MZUSP 127759, 306 mm TL. C. P. rutrum, MZUSP 9953, 235 mm TL. at1, accessory terminal 1 cartilage; at2, accessory terminal 2 cartilage; dcf, distal cleft; dd, dermal denticles; hp, hypopyle; pcf, proximal cleft; pecten; pj, projection; pr, pseudorhipidion. Scale bar = 10 mm.

Clasper skeleton consists of a slender axial cartilage and considerably tapered distal end in P. lentiginosa and P. rutrum, while slightly tapered distally in P. extenta (Figs. 19–20). Dorsal marginal cartilage distally tapered, reaching the level of the articulation between ventral marginal and ventral terminal cartilages in P. extenta, while in P. lentiginosa and P. rutrum it is truncated with distal margin articulated with proximal margin of dorsal terminal 2 cartilage, which is absent in P. extenta (Figs. 19–20). Dorsal terminal 2 cartilage dorsoventrally flattened, plate-shaped with a narrow proximal margin and large medial region in P. lentiginosa, while triangular in P. rutrum, with a large proximal margin and tapered distal end. Ventral marginal cartilage elongated and uniform, in P. lentiginosa, and distally robust, in P. rutrum, articulating with the proximal margins of accessory terminal 1 cartilage and accessory terminal 2 cartilage; in P. extenta, it is uniformly narrow up to the level of the articulation with ventral terminal, where it expands slightly as it extends distally continuously to the accessory terminal 1 cartilage. Ventral terminal cartilage elongated and spoon-like, in P. extenta and P. lentiginosa, and short with blade-shaped distal end in P. rutrum; proximal margin articulated with ventral marginal cartilage, in P. extenta, while proximal margin articulated with accessory terminal 1, in P. lentiginosa and P. rutrum. Accessory terminal 2 cartilage projected transversely to lateral and tapered distally in P. lentiginosa, flattened dorsoventrally and tapered distally in P. rutrum and absent in P. extenta. Accessory terminal 1 cartilage tapering anteroposteriorly, projected transversely to lateral at its medial portion, and with a rounded posterior tip, in P. extenta; proximally robust and distally acute, in P. lentiginosa; dorsoventrally flattened and with a tapered distal tip, in P. rutrum (Figs. 19–20).

FIGURE 19| Skeletal anatomy of left clasper of Psammobatis species. A. P. extenta, DBAV.UERJ uncatalogued, 262 mm TL, dorsal view. B. P. lentiginosa, MZUSP 127759, 306 mm TL, ventral view. C. P. rutrum, MZUSP 9953, 235 mm TL, dorsal view. at1, accessory terminal 1 cartilage; at2, accessory terminal 2 cartilage; ax, axial cartilage; dm, dorsal marginal cartilage; dt2, dorsal terminal 2 cartilage; vm, ventral marginal cartilage; vt, ventral terminal cartilage.

FIGURE 20| Skeletal anatomy of left clasper of Psammobatis species; ventral view. A. P. extenta, DBAV.UERJ uncatalogued, 262 mm TL. B. P. lentiginosa, MZUSP 127759, 306 mm TL. C. P. rutrum, MZUSP 9953, 235 mm TL. at1, accessory terminal 1 cartilage; at2, accessory terminal 2 cartilage; ax, axial cartilage; dt2, dorsal terminal 2 cartilage; vm, ventral marginal cartilage; vt, ventral terminal cartilage. Scale bar = 5 mm.

Discussion​

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Although coloration has been widely used to distinguish Psammobatis species, misidentification persisted mainly between adult specimens of P. extenta and P. rutrum (Miranda Ribeiro, 1907; Roux, 1979) and juveniles of P. extenta and P. lentiginosa. However, the presence of an ocelli on the posterior region of pectoral fins of P. extenta, in both juveniles and adults, proved to be a useful and distinctive character for this species. Moreover, P. extenta and P. rutrum differ from each other by the distribution pattern of spots on the orbital region; spots more concentrated around the eyes in P. extenta while more anteriorly distributed in P. rutrum. In addition, P. rutrum is the only species of the three analyzed herein that presents a dark spot in the center of each pectoral fin throughout its ontogeny.

It is important to note that the observations were made on specimens preserved in alcohol and differences in color tones should not be considered in full. McEachran (1983) described P. rutrum with similar spots to P. extenta, however, this characteristic was not mentioned by Paragó (2001) and Gomes (2002) neither observed in this study. In addition, Gabbanelli et al. (2022) reported P. lentiginosa with a tail coloration pattern similar to that observed in P. extenta in our analyses. Gabbanelli et al. (2022) also pointed out the darkening in the background color of specimens that have been refrigerated.

Distinctive features of great relevance for the identification of P. extenta are the denticles observed along spermatic groove and the so-called mid-pectoral thorns (Paragó, 2001; Gomes, 2002; Gomes et al., 2019; this study). A detailed description and illustration of mid-pectoral thorn using a scanning electron microscope (SEM) is provided herein, which enables the visualization of a well-defined star-shaped base and a straight rostral-caudal orientation. Although immature specimens and some adults may lack these pectoral denticles, this characteristic can be regarded as useful in differentiating P. extenta and P. rutrum (Paragó, 2001). The latter also displays pectoral denticles, which can be confused with the mid-pectoral thorns. However, the stellate base loses some of its shape, and the orientation becomes more inclined about the pectoral posterior margin.

The interruption of the three thorn rows (middorsal and dorsolateral) just after the scapular region is only observed in individuals of P. rutrum and is, therefore, a diagnostic feature of this species (Figueiredo, 1977; McEachran, 1983; Paragó, 2001; Gomes, 2002). However, other patterns of interruption of these thorns have also been observed herein. Specimens of P. extenta may have a short interruption in the middorsal row while the dorsolateral rows remain continuous. On the other hand, the interruption in the middorsal row may be more frequent in P. lentiginosa and the pattern of the rows of spines on the tail is more organized when compared to the other two species. In addition, although the reduction or absence of denticles is described as a character of P. lentiginosa (Paragó, 2001; Gomes, 2002; Gomes et al., 2019), in this species, we observed that well-developed dermal denticles are frequent along dorsolateral rows, forming a rough band.

Larger adult males of P. lentiginosa often have a significant reduction in the number of thorns on the pectoral posterior region and pelvic fins, contributing to a smoother appearance. However, this is not observed in females, as there is a distinctive presence of prickles on the pelvic posterior lobes (Paragó, 2001; Gomes, 2002). An interorbital thorn was also observed in a single adult male specimen of P. lentiginosa (MZUSP 127757, 406 mm TL), although no record of interorbital thorns within the genus is found in the literature. Therefore, the occurrence of this characteristic may be related to the size and maturity stage of specimens. However, it is worth noting that McEachran (1983) did not mention an interorbital thorn; the largest male specimen examined of P. lentiginosa was 435 mm TL. In the thorns of the posterior pectoral region, some patterns and differences can be observed between the two other species. In P. extenta, thorns are smaller and less clustered whereas in P. rutrum, thorns are greater and more aggregated.

According to Paragó (2001) and in contrast to McEachran, Dunn (1998), the nuchal and scapular thorns form a triangular grouping. In addition, distinctive patterns in this organization were identified between species. In P. extenta, scapular thorns that form the triangle base tend to be grouped more closely from each other while in P. rutrum, these same thorns are more widely spaced, resulting in a larger, arc-shaped triangular base. In specimens of P. lentiginosa, the pattern is more similar to P. extenta but with a reduction in the number of thorns. According to Paragó (2001), numbers of orbital thorns are constant between species, while Gomes (2002) observed a reduction in the number of thorns for P. rutrum. Here, we observed a numerical reduction in specimens of P. lentiginosa, especially in the postorbitals, spiracles, and midorbitals, which were often absent. It is also possible to notice a greater number of rostral and malar spines in P. extenta and P. rutrum when compared to P. lentiginosa.

In terms of morphometrics, the three species showed significant differences between males and females. The values were higher for males in the measurements preorbital length (in P. lentiginosa), mouth width, and eye diameter (in P. extenta and P. rutrum); while all the other measurements (prenasal length, preoral length, distance between first gill slits, distance between fifth gill slits, and disc width at eye line) showed higher values in females. Braccini, Chiaramonte (2005) found differences in growth in mouth width and eye diameter, especially in males of P. extenta. The higher prenasal length and preoral length values in females of the three species may be related to the sexual dimorphism also found in the mouth shape, as well as in the shape and size of teeth (Ishiyama, 1958; Feduccia, Slaughter, 1974; Braccini, Chiaramonte, 2002; Braccini, Chiaramonte, 2005; Brum-Neto, Lucena, 2020). Sexual dimorphism related to distance between first gill slits (only in P. rutrum) and distance between fifth gill slits indicates a greater abdominal region of females, which may be associated with reproduction due to the need for a larger space to accommodate eggs (Martins, Oddone, 2017). Regarding disc width at eye line, this measurement can be related to the concave shape of disc anterior margin of adult males, which has already been observed by previous authors (Norman, 1937; McEachran, 1983; Paragó, 2001).

Regarding the distinction between P. lentiginosa and P. extenta, 10 measurements were significant, with all values higher for P. lentiginosa. As for P. extenta and P. rutrum, seven significant variables were higher in P. rutrum and were related to the disc, snout, and eye diameter. P. rutrum and P. lentiginosa differed in 12 variables, where only distance from first dorsal fin origin to posterior end of caudal fin and fifth gill slit width were greater for P. rutrum.

Neurocranium anatomy shows a very characteristic shape for the three species. However, we observed some differences mainly in the anterior fontanelle and the position of the orbital foramina. The position and shape of the posterior nasal cartilage was also found to vary between P. extenta and P. rutrum. Additionally, the basal fenestrae are narrower and more rectangular in P. extenta, contrasting with the kidney-shaped ones described by McEachran (1983) and McEachran, Dunn (1998).

Clasper external morphology of the three species differs in the position of spermatic groove (lateral in P. lentiginosa and P. rutrum, and dorsal in P. extenta) and the presence of dermal denticles (present only in P. extenta). As for the skeleton, P. lentiginosa and P. rutrum are more similar to each other, with dorsal terminal 2 cartilage covering a large part of the terminal elements and the absence of a dorsal terminal 1 cartilage, as described by McEachran (1983), Menni (1972), Moreira (2017). In contrast, P. extenta has a small number of terminal cartilages, not presenting a dorsal terminal 1, dorsal terminal 2, and accessory terminal 2. In addition, McEachran (1983) also pointed out an expansion of the ventral marginal in place of the accessory terminal 1 cartilage, which can also be interpreted, as observed by Menni (1972), Moreira (2017) and also in this study, as the accessory terminal 1 cartilage fused with the ventral marginal.

Concerning geographical distribution, all three species prefer warmer waters, but P. lentiginosa can also be found in intermediate waters (Mabragaña, 2007; Mabragaña et al., 2012). Psammobatis rutrum seems to be less abundant on the Argentinean coast, as Mabragaña (2007) only caught specimens as far south as Uruguay, indicating the rare appearance of this species in the region. On the other hand, P. lentiginosa, according to Mabragaña (2007), Mabragaña et al. (2012) and Cousseau et al. (2007), occurs with locality interruptions. Different factors can act as population barriers, such as salinity, temperature, food availability, and geographical barriers. As pointed out by Sabadin et al. (2020), chondrichthyan populations can be affected by the mouth of Rio de la Plata, between Uruguay and Argentina, and also by the confluence of waters that forms the Subtropical Platform Front, in Rio Grande do Sul, Brazil.

These analyses allowed us to correct the identification of the specimens MNRJ 32626, 33565, and 49365 and MZUSP 127757 and 127758. No considerable population patterns were found in association to coloration and dermal denticles. Considering the intraspecific variation found in the three species, studies with a greater number of specimens are needed to investigate population patterns, also considering additional structures (e.g., teeth).

Taxonomic key to the Brazilian species of Psammobatis

1a. No spots forming patterns around the orbits; females with prickles on the pelvic posterior lobe……………….. 2

1b. Presence of spots forming patterns around the orbits; females without prickles on the pelvic posterior lobe……………….. 3

2a. Presence of symmetrically arranged ocelli on the pectoral fin; a lighter triangular spot between the spiracles of adults; dark spot on the pectoral region and at the intersection with the pelvic fins of adults and juveniles; presence of thorns on the pectoral fin, resulting in a rough texture……………….. P. bergi

2b. Ocelli not symmetrically arranged on the pectoral fin; no lighter triangular spot between the spiracles of adults; no dark spot on the pectoral region or at the intersection with the pelvic fins of adults and juveniles; reduction or absence of thorns on the pectoral fin, resulting in a smooth appearance; presence of a rough band in the dorsal central region, contrasting with the smooth appearance of the pectoral fins; males with reduced or absent thorns in the pectoral posterior region……………….. P. lentiginosa

3a. Presence of a mid-pectoral thorn with the tip oriented posteriorly; continuous rows of dorsal thorns posterior to the scapular region; presence of more grouped thorns in the pectoral posterior region; spermatic groove of claspers dorsally positioned and with dermal denticles; dorsal coloration with spots forming circular or non-circular edges, smaller than or equal to the eye diameter; presence of ocelli on the pectoral posterior region (in adults and juveniles); no whitish spots randomly distributed on dorsal surface; no dark spot on the pectoral central region of adults……………….. P. extenta

3b. No mid-pectoral thorn; interruption of the dorsal thorn rows posterior to the scapular region; presence of more widely spaced thorns in the posterior region of the pectoral fin; spermatic groove of claspers positioned laterally, with no dermal denticles; dorsal coloration without spots forming circular edges; no ocelli on the pectoral posterior region; presence of whitish spots randomly distributed on dorsal surface; dark spot on the pectoral central region of adults and juveniles……………….. P. rutrum

Acknowledgments​

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We would like to thank Hugo Santos (UERJ) for donating material, references and valuable comments to this work. To Marcelo Britto and Cristiano Moreira (MNRJ) for the permission to visit the fish collection and examine specimens under their care. To Alessio Datovo and Michel Gianeti and (MZUSP) for the loan of specimens. To Marcelo Melo (IO-USP) for the loan of specimens recently collected by the DEEP-OCEAN project (FAPESP process number 17/12909–4). We also thank Leila Pessôa, Cleo Oliveira (UFRJ) and Elisabeth Henschel (UFV) for their valuable contributions to the improvement of this manuscript. To Luis Otavio (LUCHM), Jean Pierre, and Olivia Pereira (CENABIO), for preparing skin samples and SEM-images. Part of this work was included in the monograph of EFS, which was supervised by KDAS and financially supported by Programa Institucional de Bolsas de Iniciação Científica – Conselho Nacional de Desenvolvimento Científico e Tecnológico (PIBIC-UFRJ).

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Authors

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Evelyn F. Santiago¹ and Karla D. A. Soares¹

^[1]    Laboratório de Chondrichthyes, Departamento de Zoologia, Instituto de Biologia, Universidade Federal do Rio de Janeiro, Av. Carlos Chagas Filho, 373, 21941-902 Rio de Janeiro, RJ, Brazil. (EFS) evelynfsantiago@gmail.com (corresponding author), (KDAS) karlad.soares@yahoo.com.br.

Authors’ Contribution

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Evelyn F. Santiago: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Supervision, Visualization, Writing-original draft, Writing-review and editing.

Karla D. A. Soares: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Supervision, Validation, Visualization, Writing-original draft, Writing-review and editing.

Ethical Statement​

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Not applicable.

Competing Interests

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The author declares no competing interests.

How to cite this article

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Santiago EF, Soares KDA. Taxonomy and morphology of three species of Psammobatis distributed in the Southwestern Atlantic Ocean (Rajiformes: Arhynchobatidae) with notes on intraspecific variation. Neotrop Ichthyol. 2025; 23(2):e240074. https://doi.org/10.1590/1982-0224-2024-0074

Copyright​

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This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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© 2025 The Authors.

Diversity and Distributions Published by SBI

Accepted March 11, 2025

Submitted July 31, 2024

Epub June 06, 2025