Ancistrus brevipinnis (Regan, 1904)

Widholzer, Ronaldo L., Borsoi, Jessica, Reis, Roberto E. & Lehmann A., Pablo, 2024, A new species of Ancistrus (Siluriformes: Loricariidae), with a redescription of Ancistrus brevipinnis and further evidence of hidden diversity in the laguna dos Patos system, Brazil, Neotropical Ichthyology (e 230078) 22 (1) : -

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 wellisolated 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.

Percent of standard length

Abdominal length 16.6 20.1 18.5 1.1 15.8 21.2 18.8 1.6 Adipose fin to caudal fin distance 17.3 20.8 18.7 1.1 18.6 22.3 20.2 1.2 Adipose-fin spine length 8.9 13.3 10.6 1.4 9.9 13.0 11.3 1.1 Anal fin to caudal fin distance 30.2 35.9 33.3 2.1 33.3 36.5 34.7 1.0 Anal-fin unbranched ray length 6.8 12.2 8.5 1.6 6.3 10.6 9.0 1.4 Body depth at dorsal-fin origin 15.9 19.8 17.7 1.4 16.3 22.6 18.9 1.8 Body width at dorsal-fin origin 27.8 32.4 30.1 1.9 28.2 33.0 30.1 1.6 Caudal peduncle depth 8.8 11.5 10.0 0.9 10.6 12.9 12.1 0.7 Caudal peduncle length 30.1 34.1 32.3 1.3 30.5 36.4 33.4 1.7 Cleithral width 30.3 34.1 32.1 1.6 32.8 37.5 34.8 1.5 Dorsal fin to adipose fin distance 12.5 16.0 14.1 1.1 11.4 16.2 13.3 1.2 Dorsal-fin base length 20.0 22.6 21.2 0.9 19.6 24.4 22.3 1.4 Dorsal-fin spine length 21.1 25.3 22.9 1.3 22.4 27.8 24.9 1.7 Head length 30.2 33.3 32.2 0.9 32.0 37.8 34.4 1.8 Interbranchial distance 14.5 20.1 17.2 1.5 17.4 20.4 18.9 1.0 Lower caudal-fin ray length 24.7 30.4 27.7 2.1 23.5 31.8 27.3 2.7 Pectoral-fin spine length 28.1 32.9 29.9 1.5 24.6 36.5 31.2 3.1 Pectoral fin to pelvic fin distance 21.1 25.7 23.6 1.6 19.8 26.0 23.0 1.6 Pelvic-fin unbranched ray length 21.0 25.3 22.8 1.4 21.4 29.1 25.1 2.0 Predorsal length 41.8 45.7 43.8 1.3 41.4 47.7 44.6 2.1 Supracleithral width 25.2 29.7 27.1 1.6 27.8 32.2 29.6 1.5 Upper caudal fin ray length 19.9 24.3 22.2 1.3 18.8 25.5 21.8 1.9

Percent of head length

Head depth at opercle 47.6 53.1 50.0 2.2 45.7 52.4 49.0 1.9 Internostril distance 17.0 22.8 19.8 2.0 15.8 18.7 17.3 1.0 Interorbital distance 38.0 43.3 40.8 2.1 31.9 39.3 35.9 2.1 Mandibulary ramus 15.2 20.2 18.3 1.5 19.1 23.9 21.6 1.6 Snout tip to ventral branchial opening 64.9 70.6 68.8 1.9 65.7 76.3 70.4 3.0 Orbital diameter 15.9 20.5 17.7 1.4 13.7 19.7 17.3 1.6 Snout length 58.8 64.6 62.2 1.7 54.5 67.7 62.1 4.4

Count

Mode Mode Premaxillary teeth 46 71 69 44 70 57 Dentary teeth 44 76 64 40 77 59 Plates in dorsal lateral series 21 22 21 22 21 21

Plates in median lateral series 20 23 23 21 23 23

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).