Loricariidae is the most diverse of the 40 siluriform families with 1,044 species (Fricke et al., 2023). The genus Ancistrus Kner, 1854 is the second most speciose in the family with 76 species (Fricke et al., 2023) inhabiting lotic environments throughout the Neotropics, with the greatest diversity occurring in the northern region of South America. Of those species, 14 have been described in the last 10 years, and descriptions prior to 1950 are not very informative, preventing the accurate identification of many species (Neuhaus et al., 2022). Ancistrus brevipinnis (Regan, 1904) is the only species so far recognized in the laguna dos Patos drainage basin in South Brazil. Its original type-locality given by Regan (1904) was [State of] Rio Grande do Sul, which was later restricted to the laguna dos Patos hydrographic system by Malabarba (1989). Based on information in the fish catalog of the Natural History Museum of London associated with historical records of Sebastian Wolff and Hermann von Ihering, former residents of the municipality of São Lourenço do Sul and collectors of the holotype of Ancistrus brevipinnis, its type-locality can be further restricted to the rio Camaquã sub-basin of the laguna dos Patos.

Ancistrus brevipinnis was poorly described, based on a single individual, and clearly needs a thorough redescription since morphological variation currently observed in the laguna dos Patos system suggests the existence of previously undetected diversity. Comparison of different populations of Ancistrus from the laguna dos Patos system revealed that fish from the rio Vacacaí are clearly distinct from those of remaining sub-basins, and here we describe them as a new species. In addition, the population of A. brevipinnis from the rio Camaquã is distinguishable from the populations in more northern tributaries of the laguna dos Patos, chiefly the rio Jacuí basin, and we provide a redescription of A. brevipinnis based on specimens from the newly restricted type-locality, the rio Camaquã sub-basin.

Measurements were obtained with a 0.1 mm precision digital caliper under a stereomicroscope when necessary. The 33 measurements and counts follow Bifi et al. (2009) with the addition of distance between the end of dorsal-fin base and the origin of the adipose fin; and body depth at origin of dorsal fin. All measurements and counts were taken on the left side of each individual, except when that side was damaged, and presented as percent of standard length (SL) or head length. A Linear Discriminant Analysis (Fisher, 1936) was performed with ratios of all measurements on the standard length in Python 3.8 with scripts adapted from Widholzer (2023). In the search for diagnostic characters, qualitative features of external anatomy (e.g., color pattern, shape and arrangement of teeth, body and fin shape, and presence/absence of chromatophores) were analyzed. Osteological characters were observed in specimens cleared and double stained (c&s) according to Taylor, Van Dyke (1985). Vertebral centra were counted in c&s specimens only and include five centra modified into the Weberian apparatus and one compound caudal centrum (PU1+U1). Identification and counts of dermal plates follow the serial homology scheme proposed by Schaefer (1997).

Institutional abbreviations follow Sabaj (2020), except for Museu de Zoologia da Universidade do Vale do Rio dos Sinos (UNISINOS), São Leopoldo, Rio Grande do Sul, Brazil (MZU). In addition, we conducted field expeditions to collect living specimens for tissue (tis) sampling and color assessment between May and November of 2022. For all species already described and with the exception of Ancistrus brevipinnis, A. multispinis and A. taunayi, all other outgroup comparisons were made based on their morphological information in the original description.

Genetic sequence of gene coI from selected paratype follows GenSeq nomenclature (Chakrabarty et al., 2013). Total genomic DNA was extracted using the DNeasy blood and tissue extraction kit (Qiagen) from muscle samples fixed in 95% ethanol and stored at -20°C. DNA sequences of the mitochondrial coIgene were amplified by PCR using primers Fish-F1 and Fish-R1 (Ward et al., 2005), under the following protocol: an initial denaturation step of 3 minutes at 95°C followed by 35 cycles of 94°C for 30 sec, annealing at 52°C for 40 sec, and extension at 72°C for 1 min, followed by a final 5 min extension step at 72°C. PCR products were purified and sequenced at Functional Biosciences Inc., Madison, USA. Sequences were edited in Geneious v. 8.0.5 and aligned with the Muscle algorithm as implemented in MEGA v. 11. A genetic distance matrix was built under the Kimura 2-parameter model and a Maximum Likelihood tree was calculated under the General Time Reversible model with Gamma distribution and invariant sites, and the bootstrap calculated from 500 replicates, again using MEGA v. 11. DNA sequences of gene coIused in this study were uploaded to the Genbank database and have the following accession codes (Ancistrus brevipinnis, OR242765-OR242767, A. aff. brevipinnis, OR242763-OR242764, A. taunayi Miranda Ribeiro, 1918, OR250757, A. multispinis (Regan, 1912), OR242730, and Ancistrus sp. n. described below, OR250758). A sequence of Ancistrus aguaboensis Fisch-Muller, Mazzoni & Weber, 2001, used to root the ML tree, was obtained from the Genbank (MK464026).

Ancistrus megacanthus, new species

urn:lsid:zoobank.org:act:6E583531-02DB-4557-8F3E-837D56B190D3

(Figs. 1‒2; Tab. 1)

Holotype. MCP 19582, male, 96.8 mm SL, Brazil, Rio Grande do Sul, São Gabriel,rio Vacacaí on road RS-630, tributary to rio Jacuí, laguna dos Patos system, 30°27’18”S 54°22’26”W, 14 Jan 1997, L. R. Malabarba, J. A. Gomes & V. A. Bertaco.

Paratypes. Brazil, Rio Grande do Sul, rio Vacacaí basin, laguna dos Patos system: MCP 54919, 5, 47.7‒74.5 mm SL (all measured) + 1 c&s, 54.5 mm SL, collected with holotype. MCP 16294, 6, 85.3‒124.4 mm SL (all measured), MZUSP 128046, 1, 120.2 mm SL (measured), UFRGS 29411, 1, 101.1 mm SL (measured), Caçapava do Sul, arroio Pessegueiro, ca. 30º28’S 53º37’W, 15 Apr 1993, A. Ramires. MCP 54883, 1 (tissue sample), 39.4 mm SL (measured), São Gabriel, arroio Cambaizinho on road BR-290, 30°20’23”S 54°03’07”W, 5 Jul 2022, R. Widholzer & M. Haas. MCP 54898, 2, 33.7‒44.1 mm SL (1 measured, 44.1 mm SL), São Gabriel, arroio Cambaizinho on road BR-290, 30°20’23”S 54°03’07”W, 4 Nov 2022, R. Widholzer & M. Haas.

Genseq-2 coI. Sequence deposited in GenBank (MCP 54883 GenBank accession code OR250758).

Diagnosis. Ancistrus megacanthus differs from non-Andean congeners (except A. abilhoai Bifi, Pavanelli & Zawadzki, 2009, A. agostinhoi Bifi, Pavanelli & Zawadzki, 2009, A. brevifilis Eigenmann, 1920, A. brevipinnis, A. cirrhosus (Valenciennes, 1836), A. cuiabae Knaack, 1999, A. hoplogenys (Günther, 1864), A. kellerae de Souza, Taphorn & Armbruster, 2019, A. leucostictus (Günther, 1864), A. lithurgicus Eigenmann, 1912, A. luzia Neuhaus, Britto, Birindelli & Sousa, 2022, A. maximus de Oliveira, Zuanon, Zawadzki & Rapp Py-Daniel, 2015, A. mullerae Bifi, Pavanelli & Zawadzki, 2009, A. multispinis, A. nudiceps (Müller & Troschel, 1849), A. patronus de Souza, Taphorn & Armbruster, 2019, A. saudades de Souza, Taphorn & Armbruster, 2019, A. taunayi, A. stigmaticus Eigenmann & Eigenmann, 1889, A. trinitatis (Günther, 1864), and A. yutajae de Souza, Taphorn & Armbruster, 2019)by adult males – those with well-developed snout tentacles – having the pectoral-fin spine long, exceeding half length of the pelvic-fin leading ray (vs. pectoral-fin spine short, not reaching half length of the pelvic-fin leading ray). It differs from those species (except A. yutajae), and including all congeners from Rio Grande do Sul (A. brevipinnis, A. multispinis, and A. taunayi), by having dorsal and caudal fins plain dark brown to black, without lighter spots or bands (vs. lighter spot or bands on dorsal and caudal fins), and differs from A. brevipinnis and A. yutajae by having a dark brown to black background body color (vs. light brown body). Additionally, the new species is distinguished from A. taunayi by having small white to yellow dots on dorsal surface (vs. dorsal surface with light brown to pale yellow vermiculated spots). Ancistrusmegacanthus is further distinguished from A. taunayi by having four branched rays on the anal fin (vs. three branched rays).

Description. Morphometric data in Tab. 1. Body and head depressed. Dorsal profile of body and head convex from tip of snout to dorsal-fin origin, slightly concave to straight from that point to origin of adipose fin, concave from end of adipose fin to origin of caudal fin. Ventral profile of body straight, body height begins to decrease at pelvic girdle. Body covered with bony plates except along dorsal-fin base and ventral surface between tip of snout and anal-fin origin. Median series with 22‒24(13, 23*) lateral plates; lateral-line canal complete and uninterrupted. Three* predorsal plates, seven* plates at base of dorsal fin, four* plates between dorsal and adipose fins and 8*(6), 7(5) or 6(2) plates between adipose fins and caudal fins. Fin rays and body plates covered by small, caudally directed odontodes in regular rows, larger on fin spines.

Snout rounded, with wide bare anterior margin, posteriorly limited by dermal plates of varying sizes. Cutaneous tentacles present on lateral, anterior and middorsal portions of snout of males, sometimes branched and forming “Y” pattern. In females, tentacles smaller and usually arranged in pairs on sides of snout. Eye large 13.4‒22.1% (17) of head length, located laterodorsally on head. Orbit delimited dorsally by sphenotic and frontal, anteriorly by prefrontal plate, ventrally by infraorbitals IV and V, and posteriorly by infraorbital VI. Naris located dorsally on head, with tubular expansion of skin, delimited dorsally by frontal, anteriorly by infraorbital II and III, laterally by prefrontal plate and nasal bone. Interorbital region slightly convex to flat. Exposed part of operculum almost always triangular, rounded anteriorly. Dermal plates of different sizes and shapes arranged in post-opercular area, contiguous to compound pterotic. Nine to 12(13) strong retractable odontodes with sickle-shaped claws at extremity in opercular region.

Lower lip not reaching anterior margin of pectoral girdle. Lower lip with papillae randomly distributed throughout surface. Maxillary barbel short and free. Short mandibulary ramus, 12.6‒19.6% (17) of head length; premaxillary tooth row of same length or slightly shorter. Teeth numerous, 38‒67(17) in premaxilla and 32‒68(13) in dentary, bicuspid, with reduced lateral cusp and larger, wider mesial cusp.

Dorsal-fin spine elongated, soft rays almost reaching or reaching to adipose-fin origin when depressed; pectoral-fin spine long, exceeding half-length of pelvic-fin unbranched ray on adult males; reaching first third of pelvic fin in females. Pelvic fin reaching middle of anal-fin length. Caudal fin truncated, with lower leading ray longer than upper. All branched fin rays doubly branched near apical end. Dorsal fin with II+7(17) rays; pectoral fin I+6(17) rays; pelvic fin i+5(17) rays; anal fin i+4(17) rays; caudal fin i+14+I(17) rays.

Sixth vertebral centrum (first after Weberian apparatus) with enlarged rib. Seventh vertebra without rib and supporting first dorsal-fin pterygiophore. Eight following vertebral centra with thin ribs and supporting dorsal-fin pterygiophores. Total vertebrae 28(1).

Coloration in alcohol. Dorsal and ventral region of body dark brown to black. Well-defined white to yellowish white dots, usually smaller than pupil diameter, on dorsal and lateral region of body, sometimes in ventral region, usually not visible in poorly preserved specimens. Slightly lighter brown bar on terminus of caudal peduncle. Rays and interradial membranes of paired fins with dark coloration similar to body and no or inconspicuous light dots. Dorsal, adipose and caudal fins plain dark brown to black. Upper and lower tip of caudal-fin leading rays and outer branched rays with small light termination (Fig. 1).

Coloration in life. Body dark brown to black with pale yellow dots, usually smaller than pupil diameter, along body; paired fins with yellow dots, dorsal fin with few inconspicuous light dots on unbranched ray, adipose and caudal fins unmarked. Lighter brown bar on terminus of caudal peduncle. Tip of upper and lower leading rays and outer branched rays of caudal fin with conspicuous yellow spots (Fig. 2).

Sexual dimorphism. Adult males have more numerous and larger snout tentacle than females and larger pectoral-fin spines, usually exceeding half-length of the pelvic-fin unbranched ray and reaching the first third of pelvic fin in females.

Geographical distribution.Ancistrus megacanthus is known from three localities in the rio Vacacaí sub-basin of the rio Jacuí basin, laguna dos Patos hydrographic system (Fig. 3).

Ecological notes. The new species occurs in creeks at altitudes close to 100 m above sea level, with swift waters and rocky to gravelly bottom (Fig. 4). These water courses are in the Pampa biome, in a savannah formation with predominance of herbaceous vegetation and trees restricted to river banks, and with soils characterized by being clayey and gravelly, typical of the Precambrian Sul-Riograndense Shield terrains.

Etymology.Ancistrus megacanthus, latinized from Greekmegas (megas), large, great and akanthos(akanthos), thorn, spine, in reference to the large pectoral-fin spines of the new species. A noun in apposition.

Conservation status. Ancistrus megacanthus is known from three localities in the rio Vacacaí drainage, with an Extension of Occurrence (EOO) estimated by the maximum convex polygon around the Vacacaí-Mirim sub-basin of 11,177 km2. Main diffuse threats in the area are the transformation of the lotic environment to lentic habitats (e.g., by the construction of dams) and the use of agricultural pesticides. As no specific threats to the species were detected, it is provisionally assessed as Least Concern (LC) according to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, 2022).

Ancistrus brevipinnis (Regan, 1904)

(Figs. 5‒7; Tab. 2)

Chaetostomus cirrhosus (non Valenciennes, 1836) Boulenger, 1891:234, pl. 26, fig. 1 (listed and illustrated from Rio Grande do Sul State, Brazil).

Xenocara brevipinnis Regan, 1904:257 (type-locality: [State of] Rio Grande do Sul, Brazil. Holotype: BMNH 1891.3.16.76, female, 79.9 mm SL). Type-locality herein restricted to the rio Camaquã basin, Rio Grande do Sul, Brazil.

Description. Morphometric data in Tab. 2. Body and head depressed. Dorsal profile of body and head convex from tip of snout to dorsal-fin origin, slightly concave to straight from that point to origin of adipose fin, concave from end of adipose fin to origin of caudal fin. Ventral profile of body straight, body height begins to decrease at pelvic girdle. Body covered with bony plates; plates absent along dorsal-fin base and ventral surface between tip of snout and anal-fin origin. Median series with 22‒24(11) lateral plates; lateral-line canal complete and uninterrupted. Three (11) predorsal plates, seven (11) plates at base of dorsal fin, four (11) plates between dorsal and adipose fins and 6(1), 7(8) or 22(2), plates between adipose fins and caudal fins. Fin rays and plates covered by small, caudally directed odontodes in regular rows, larger on fin spines.

Snout rounded, with wide bare anterior margin, limited posteriorly by dermal plates of varying sizes. Cutaneous tentacles present on lateral, anterior and middorsal portions of snout of males, sometimes branched and forming “Y” pattern. In females, tentacles smaller and usually arranged in pairs on sides of snout. Eye large, 13.0‒20.2% (16) of head length, located laterodorsally on head. Orbit delimited dorsally by sphenotic and frontal, anteriorly by prefrontal plate, ventrally by infraorbitals IV and V, and posteriorly by infraorbital VI. Naris located dorsally on head, with tubular expansion of skin, delimited anteriorly by nasal, posteromedially by frontal, laterally by infraorbital II and III, and posterolaterally by prefrontal plate. Exposed part of the opercle almost always triangular, rounded anteriorly. Dermal plates of different sizes and shapes arranged in the post-opercular area, contiguous to compound pterotic. Eleven to 14(11) strong retractable odontodes with sickle-shaped claws at extremity in opercular region.

Lower lip not reaching anterior margin of pectoral girdle. Lower lip with papillae randomly distributed throughout surface. Maxillary barbel short and free. Short mandibulary ramus, 12.9‒19.9% (16) of head length, premaxillary tooth row of same length or slightly shorter. Teeth numerous, 34‒57(11) in premaxilla and 33‒53(11) in dentary, bicuspid, with reduced lateral cusp and larger, wider mesial cusp.

Dorsal-fin spine elongated, soft rays not reaching adipose fin when depressed; pectoral-fin spine reaching to half-length of pelvic-fin unbranched ray in adult males; falling short or reaching to base of pelvic fin in females. Pelvic fin reaching middle of anal-fin length. Caudal fin obliquely truncated with lower leading ray longer than upper. All branched fin rays doubly branched near apical end. Dorsal fin with II+7 rays(16); pectoral fin I+5(4) or I+6(21) rays; pelvic fin i+5(16) rays; anal fin i+4 rays (16); caudal fin i+14+i rays (16).

Sixth vertebral centrum (first after Weberian apparatus) with enlarged rib. Seventh vertebra without rib and supporting first dorsal-fin pterygiophore. Eight following vertebral centra with thin ribs and supporting dorsal-fin pterygiophores. Total vertebrae 28(1).

Coloration in alcohol. Dorsal and ventral region of body brown mottled with darker brown to gray patches. Well-defined, small yellow to light brown dots on dorsal and lateral region of body, sometimes in ventral region, smaller on head and somewhat vermiculated on flanks and abdomen. Dark brown dots on fin rays and sometimes interradial membrane of all fins. Upper and lower tips of caudal-fin leading rays with small light termination (Fig. 5).

Coloration in life. Body with complex distribution of pigments, yellowish brown and brown background mottled with darker brown to gray patches and four or five big, light yellow spots dorsally. Caudal fin preceded by slanted light brown to yellow band. Head and ventral surface of body covered with light yellow dots. Dorsal, pectoral and pelvic fins yellowish brown with inconspicuous darker dots. Anal and caudal fin mostly plain light brown, upper and lower tips of caudal-fin leading and outer branched rays with small white or light yellow termination (Fig. 7).

Geographical distribution.Ancistrus brevipinnis is believed to occur in most of the laguna dos Patos tributaries (Fig. 3), but specimens used to prepare this redescription are those from the restricted type-locality, the rio Camaquã basin.

Ecological notes. Specimens of A. brevipinnis are usually found in shallow and wide creeks and rivers, predominantly formed by pebbles and rocks and swift waters.

Previously undetected diversity in the laguna dos Patos system. During the present study we observed that populations commonly identified as Ancistrus brevipinnis have remarkable morphological variation throughout the laguna dos Patos system, which suggests the existence of undetected diversity. Some of the observed variation includes the structure of the predorsal plates, which may be present as two or three series between the supraoccipital and the dorsal fin; the length of the pectoral-fin spine, which varies from falling short of the pelvic-fin base to reaching half or even exceeding half length of that fin; the number of branched rays in the pectoral fin (5 or 6); a variation in the relationship between height and length of the caudal peduncle; the body coloration, which varies from grayish brown with yellow spots evenly distributed on body, to very dark brown with barely visible yellow dots, or light brown body with yellowish-brown dots to mottled brown with darker spots and light yellow spots; the fin coloration, ranging from black without spots to dark brown with yellow spots, sometimes restricted to rays and spines, and sometimes on interradial membranes; and the tip of the adipose-fin spine, occasionally with an evident white dot.

To deal with this variation, morphometric and meristic data were obtained separately for specimens from several sub-basins of the laguna dos Patos system (Tabs. 1‒3) and neighboring basins (Tab. 4). Linear Discriminant Analysis of the morphological data from these different populations resulted in three discrete groups (Fig. 8). A well-isolated group formed by Ancistrus brevipinnis from the rio Camaquã sub-basin and the new species described above, A. megacanthus, from the rio Vacacaí sub-basin. A second cluster with the remaining A. brevipinnis populations analyzed (herein referred to as Ancistrus aff. brevipinnis) and A. taunayi from the rio Uruguay, and a third cluster with the species inhabiting the coastal rivers, A.multispinis. The LD1 axis had the caudal peduncle length (0.40) as the most strongly positive value and the head length (-0.32) as the most strongly negative value. The LD2 axis had the body width at dorsal-fin origin (0.48) as the most strongly positive variable and the caudal-peduncle length (-0.68) as the most strongly negative variable. Further on supporting the distinctiveness of the new species, this analysis also suggests that the A. brevipinnis population from the rio Camaquã basin represents a species distinct from the more northern tributaries of the laguna dos Patos.

A molecular comparison of the gene coI of those populations and other geographically close species of Ancistrus revealed the same pattern as the morphometric analysis. The genetic distance between the three specimens of Ancistrus brevipinnis from the rio Camaquã and the A. aff. brevipinnis from the Jacuí basin ranged from 2.7 to 3.2%, numbers similar or greater than the distance between the other geographically close species (Tab. 5). A Maximum Likelihood tree of the same sequences shows the A. brevipinnis from the rio Camaquã more closely related to A. megacanthus (Fig. 9), while the A. aff. brevipinis was revealed more closely related to A. taunayi from the rio Uruguay basin. The tree species was rooted in A. aguaboensis from the Amazon basin.

Material examined. Brazil, Rio Grande do Sul, laguna dos Patos system, rio Camaquã basin: MCP 25948, 21, 22.9‒51.3 mm SL (1 measured, 51.3mm SL), rio dos Carros, Lavras do Sul, 30°46’02.42”S 53°48’23.04”W. MCP 25902, 11, 24.8‒65.9 mm SL (2 measured, 51.0‒55.2 mm SL) + 1 c&s, 56.0 mm SL, rio Marmeleiro, Lavras do Sul, 30°59’06”S 53°58’20”W. MCP 23781 7, 31.2‒65.7 mm SL (4 measured, 60.1‒65.7 mm SL), rio do Engenho, tributary to rio Velhaco, Sentinela do Sul, 30°43’48”S 51°45’24”W. MCP 54896, 4, 2 tis, 50.0‒67.5 mm SL (2 measured, 65.2‒67.5 mm SL), rio do Meio, Cristal, 30°58’10.81”S 52°10’07.42”W. UFRGS 21299, 1, 50.7 mm SL (measured), creek tributary to rio das Neves, Santana da Boa Vista, 30°51’17”S 53°13’38”W, UFRGS 21300, 5, 27.3‒72.0 mm SL (4 measured, 57.5‒72.0 mm SL), rio das Neves, Santana da Boa Vista, 30°51’45.1”S 53°13’27.8”W, UFRGS 22124, 2, 74.7‒81.3 mm SL (2 measured), rio das Neves, Santana da Boa Vista, 30°51’45.1”S 53°13’27.8”W. MCP 54985, 1 tis, arroio Bonito, tributary to arroio Velhaco, 30°43’50.87”S 51°45’23.05”W.

Genseq-3 coI. Sequence deposited in GenBank (MCP 54895, accession code OR242765, and MCP 54895, accession codes OR242766 and OR242767).

Regan (1904) described Xenocara brevipinnis with “Rio Grande do Sul” as the type-locality and later Malabarba (1989) restricted the type-locality to the laguna dos Patos system. In this study, we further restrict the type-locality of A. brevipinnis to the rio Camaquã sub-basin of the laguna dos Patos system, based on historical records of the collections of Sebastian Wolff and Hermann von Ihering, collectors of the holotype currently deposited at the Natural History Museum in London (BMNH). According to the catalog records of the NHM the shipments of freshwater fishes containing the type of A. brevipinnis sent by Wolff and von Ihering to London came mainly from the rio Camaquã and laguna dos Patos in the municipality of São Lourenço do Sul, State of Rio Grande do Sul, Brazil. This information is reinforced by the fact that von Ihering and Wolff have lived for years in the municipality of São Lourenço do Sul near the mouth of the rio Camaquã and conducted several surveys in the region. Boulenger (1891) possibly corroborates this statement in a study in which he organized an annotated list of siluriforms collected by Wolff and von Ihering in the State of Rio Grande do Sul, in which all species are easily recognized as current inhabitants of the rio Camaquã basin and nearby waterways (Pimelodella australis Eigenmann, 1917[listed as Pimelodus lateristriga Müller & Troschel, 1849], Parapimelodus nigribarbis (Boulenger, 1889), Pimelodus maculatus Lacepède, 1803, Rhamdia quelen (Quoy & Gaimard, 1824), Microglanis cottoides (Boulenger, 1891), Heptapterus mustelinus (Valenciennes, 1835), Genidens barbus (Lacepède, 1803) [listed as Arius commersonii (Lacepède, 1803)], Genidens genidens (Cuvier, 1829) [listed as Genidens cuvieri Castelnau, 1855], Callichthys callichthys (Linnaeus, 1758), Corydoras paleatus (Jenyns, 1842), Loricariichthys anus (Valenciennes, 1835), Rineloricaria sp. [listed as Loricaria lima Kner, 1853], Hisonotus nigricauda (Boulenger, 1891), Hypostomus spiniger (Hensel, 1870) [listed as Plecostomus commersonii Eigenmann & Eigenmann, 1888], Chaetostomus cirrhosus (Steindachner, 1881)[reidentified as Ancistrus brevipinnis by Regan, 1904], Pseudobunocephalus iheringii (Boulenger 1891), Cambeva sp. [listed as Trichomycterus brasiliensis Lütken, 1874], and Scleronema minutum (Boulenger, 1891)).

Both the morphometric and molecular comparisons we made with populations of what is currently known as Ancistrus brevipinnis (Fig. 8; Tab. 3) suggest that the population in the rio Camaquã is distinct from the populations inhabiting the more northern tributaries of the laguna dos Patos system, namely the rio Jacuí basin. For this reason, we provided the redescription of A. brevipinnis based on specimens from the rio Camaquã alone. We continue to work on a complete review of Ancistrus in the laguna dos Patos system, as there might exist additional undescribed diversity. Only a clear understanding of the diversity of Ancistrus in the laguna dos Patos system will permit these species to be correctly evaluated for their extinction risk and adequately protected.

Comparative material examined. All from Brazil. Rio Grande do Sul: laguna dos Patos system. Ancistrus aff. brevipinnis:Upper rio Jacuí: MCP 21216, 8, arroio Despraiado, Soledade, 28°48’26”S 52°25’47”W. UFRGS 22326, 1, rio dos Caixões, Espumoso, 29°01’54.4”S 52°49’25.1”W. MCP 22157, 6, arroio Resvalador, Nicolau Vergueiro, 28°32’54”S 52°25’59”W. MCP 22248, 5, arroio Carreta Quebrada, Passo Fundo, 28°26’48”S 52°23’04”W. MCP 22125, 3, arroio do Portão, Passo Fundo, 28°22’03”S 52°24’42”W. MCP 21254, 2, Espumoso, 28°45’51”S 52°55’10”W. MCP 22762, 6, arroio Tapiaia, Júlio de Castilhos, 29°06’49”S 53°39’04”W. MCP 50096, 1, arroio dos Macacos, Colorado, 28°28’41”S 52°57’15”W. MCP 22747, 3, rio Pinheirinho, Saldanha Marinho, 28°23’39”S 53°03’11”W. UFRGS 16737, 1, rio Quati, Mormaço, 28°38’52”S 52°37’11”W. MCP 22180, 2, rio Jacuí, Passo Fundo, 28°18’45”S 52°18’28”W. UFRGS 19984, rio Turvo, Espumoso, 28°43’47”S 52°47’40”W. MCP 22129, 2, rio da Glória, Santo Antônio do Planalto, 28°21’03”S 52°43’40”W. UFRGS 23502, 1, rio Morcego, Espumoso, 28°53’55”S 52°49’06”W. UFRGS 23505, 1, rio Morcego, Espumoso, 28°53’55”S 52°49’06”W. Lower rio Jacuí: MCP 21220, 4, Agudo, 29°31’35”S 53°18’08”W. MCP 22735, 3, arroio do Tigre, Nova Palma, 29°29’25”S 53°28’45”W. MCP 26559, 5, arroio Caembora, Nova Palma, 29°28’50”S 53°17’50”W. MCP 22721, 3, creek tributary to rio Soturno, Faxinal do Soturno, 29°32’55”S 53°27’53”W. MCP 21246, 2, arroio Linha das Flores, Agudo, 29°36’02”S 53°16’49”W. MCP 21316, 3, arroio Corupá, Agudo, 29°33’54”S 53°17’09”W. MCP 17336, 3, arroio Taquara, Minas do Leão, 30°09’02”S 52°01’58”W. MZU 2779, 1, rio Jacuí, Cachoeira do Sul, 30°06’32.7”S 52°53’14.7”W. MCP 26916, 3, arroio Patrício, Mariana Pimentel, ca. 30°21’S 51°36”W. UFRGS 6595, 1, arroio Corupá, Agudo, 29°33’54”S 53°17’09”W. UFRGS 20354, 1, arroio Giuliani, Faxinal do Soturno, 29°32’56”S 53°27’50”W. Rio Caí: MZU 2334, 1, Capela de Santana, 29°39’29.7”S 51°20’53.9”W. MCP 26011, 3, arroio Bom Jardim, Triunfo, ca. 29°51’S 51°26’W. MCP 11474, 3, arroio do Ouro, Feliz, ca. 29°18’S 51°10’W. MCP 26010, 3, arroio Bom Jardim, Triunfo, 29°50’19”S 51°23’25”W. MZU 2783, 3, Bom Princípio, 29°28’31.9”S 51°20’51.9”W. Rio Gravataí: MZU 995, 1, MZU 1021, 1, MZU 1190, 1, MZU 1549, 1, arroio Demétrio, Gravataí, 29°47’26.4”S 50°51’55.6”W. MZU 853, 1, MZU 992, 1, MZU 1034,1, MZU 1323, 1, arroio Demétrio, Gravataí, 29°47’46.4”S 50°52’21.6”W. MZU 818, 1, MZU 1046, 1, arroio Demétrio, Gravataí, 29°48’47.4”S 50°53’21.2”W. MCP 15024, 2, MCP 15464, 1, arroio Fiuza, Viamão, 30°06’07”S 51°02’41”W. MCP 54885, 1 tis, arroio Demétrio, Morungava, 29°48’43.4”S 50°53’21.2”W. Rio Pardo: MCP 21569, 2, rio Pardinho, Boqueirão do Leão, 29°18’39”S 52°31’38”W. MCP 21568, 1, arroio José Simão, Gramado Xavier, 29°15’47”S 52°32’51”W. MCP 18625, 1, rio Pardo, Candelária, 29°40’36”S 52°46’19”W. MCP 18652, 2, arroio Andreas, Vera Cruz, ca. 29°42’S 52°32’W. MCP 32503, 1, rio Pardinho, Santa Cruz do Sul, ca. 29°35’S 52°30’W. Rio dos Sinos: MCP 17634, 3, arroio do Carvalho, Caraá, 29°47’58”S 50°28’23”W. MCP 17625, 3, rio dos Sinos, Caraá, 29°46’27”S 50°26’08”W. MCP 17629, 1, rio dos Sinos, Caraá, ca. 29°47’S 50°23’W. MZU 2257, 1, rio dos Sinos, Taquara, 29°39’37.0”S 50°48’02.4”W. MCP 20163, 3, MCP 20168 5, MCP 21204, 6, arroio Feitoria, Ivoti, ca. 29°35’S 51°08’W. MZU 3172, 3, rio Paranhana, Igrejinha, 29°33’29.92”S 50°50’33.05”W. MZU 1339, 1, MZU 2439,2, arroio Solitária, Igrejinha, 29°33’10.91”S 50°50’56.39”W. MZU 1109, 2, arroio Solitário, Igrejinha, 29°33’10.26”S 50°51’12.28”W. MZU 1253, 2, arroio Solitário, Igrejinha, 29°33’45.60”S 50°50’12.28”W. MZU 942, 1, arroio Solitário, Igrejinha, 29°34’37.84”S 50°49’16.49”W. MCP 2201, 3, arroio Solitário, Igrejinha, 29°34’37.26”S 50°49’17.83”W. MZU 2285, 2, rio da Ilha, Taquara, 29°33’13.99”S 50°37’38.39”W. MZU 1415, 1, MZU 840, 1, rio dos Sinos, São Leopoldo, ca. 29°45’S 51°08’W. MCP 2270, 3, arroio Grande, Taquara, 29°45’10.2”S 50°45’10.8”W. MCP 54882, 1 tis, arroio Solitário, tributary to rio Paranhana, Igrejinha, 29°33’29.9”S 50°50’32.9”W. Rio Taquari-Antas: MCP 32351, 1, arroio São Tomé, São Francisco de Paula, 28°53’20.78”S 50°37’08.42”W. MCP 26759, 3, arroio Pessegueiro, Barros Cassal, 29°05’04”S 52°36’02”W. MCP 17501, 3, arroio Castelhano, Venâncio Aires, 29°32’59”S 52°16’59”W. MCP 21212, 7, arroio Jeremias, Arvorezinha, 28°49’44”S 52°14’35”W. MCP 22208, 6, arroio Jaboticaba, Vila Flores, 28°52’43”S 51°32’05”W. MCP 21676, 3, arroio Jabuticaba, Veranópolis, 29°01’15”S 51°34’55”W. MCP 21205, 4, arroio Três Pontes, Arvorezinha, 28°48’24”S 52°18’14”W. MCP 25676, 3, rio Fão, Barros Cassal, 29°03’09”S 52°34’50”W. MCP 25572, 3 arroio Jabuticaba, Veranópolis, 29°01’13”S 51°31’41”W. MCP 22786, 1, arroio Espeto, Muitos Capões, 28°23’26”S 51°03’22”W. MCP 37936,1, rio das Antas, Veranópolis, 29°03’50”S 51°29’55”W. MCP 50178, 2, rio Taquari, Travesseiro, 29°16’42”S 52°03’33”W. MCP 32351, 2, arroio São Tomé, Capão Alto, 28°53’20.78”S 50°37’08.42”W. MCP 22240, 1, arroio Quebra Perna, São Domingos do Sul, 28°34’01”S 51°50’36”W. MCP 37688, 1, rio das Antas, Bento Gonçalves, 29°01’08”S 51°28’28”W. Coastal basins.Ancistrus multispinis:MCP 10796, 1, rio Maquiné, Maquiné, ca. 29°36’S 50°17’W. MCP 13654, 10, rio Maquiné, Maquiné, ca. 29°40’S 50°11’W. MCP 29102, 19, arroio Garapiá, Barra do Ouro, 29°30’26”S 50°14’39”W. MCP 29133 2, arroio Bananeira, Itati, 29°26’33”S 50°11’18”W. MCP 29145, 1, arroio Forqueta, Barra do ouro, 29°32’08”S 50°12’21”W. MCP 53880, 1, arroio Morro Azul, Três Cachoeiras, 29°23’57”S 49°55’00”W. MCP 53896, 9, rio Sangão, Mampituba, 29°14’19”S 49°58’29”W. UFRGS 18448, 1 tis, creek tributary to rio Maquiné, Maquiné, 29°31’26”S 50°18’47”W. Santa Catarina: Coastal basins. MCP 10639, 103, rio Jordão, Nova Veneza, ca. 28°35’S 49°27’W. MCP 19889, 1, rio Ano Bom, Corupá, ca. 26°26’S 49°16’W. MCP 29277, 1, arroio Molha Côco, Praia Grande, 29°10’27”S 49°58’26”W. MCP 31539, 2, rio Lindo, Joinville, 26°11’31”S 48°55’44”W. Rio Grande do Sul: rio Uruguay basin.Ancistrus taunayi: MZU 2413, 3, arroio Taquarembó, Dom Pedrito, 30°54’32.11”S 54°35’29.65”W. MCP 34532, 3, arroio Pinheirinho, Carazinho, ca. 28°13’S 53°06”W. MCP 41153, 6, arroio Felício, Júlio de Castilhos, 29°19’04”S 53°37’54”W. MCP 46749, 4, rio Jaguari, Lavras do Sul, 30°49’15.8”S 54°17’56.5”W. MCP 46744, 2, rio Jaguari, Dom Pedrito, 30°37’23”S 54°26’36”W. MCP 43914, 1 tis, arroio Jaguari, tributary of rio Santa Maria, Lavras do Sul, 30°49’13”S 54°17’57”W.