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), pp. 1-23 : 10-19

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.

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).

Figures

FIGURE 3 | Distribution of Ancistrus species in northern laguna dos Patos system.Ancistrus aff.brevipinnis (yellow), A. brevipinnis (turquoise), and A. megacanthus (red). T = type-locality.

FIGURE 5 | Ancistrus brevipinnis, dorsal, lateral and ventral views, MCP 25902, female, 65.9 mm SL, Brazil, Rio Grande do Sul, Lavras do Sul, rio Marmeleiro, laguna dos Patos system.

FIGURE 6 | Holotype of Ancistrus brevipinnis, BMNH 1891.3.16.76, female, 79.9 mm SL. Rio Grande do Sul, Brazil. Photograph inverted horizontally. Photo by the ACSI Project image.

FIGURE 7 | Live color pattern of Ancistrus brevipinnis. Specimens not preserved. Hemiancistrus punctulatus on background.

FIGURE 8 | Linear Discriminant Analysis of Ancistrus species in northern laguna dos Patos system. H = holotype of A. megacanthus.

FIGURE 9 | Maximum likelihood tree of samples of Ancistrus from Rio Grande do Sul, using General Time Reversible model with Gamma distribution and invariant sites (47.5%). Log likelihood -1230,53.

Tables

TABLE 2 | Morphometric data of Ancistrus brevipinnis. n = 16; SD = Standard deviation.

	Min	Max	Mean	SD
Standard length (mm)	35.8	81.3	58.6	–
Percent of standard length
Abdominal length	17.5	23.3	19.6	1.5
Adipose fin to caudal fin distance	16.2	22.9	19.8	2.0
Adipose-fin spine length	7.5	12.5	9.9	1.3
Anal fin to caudal fin distance	31.8	37.4	34.1	1.4
Anal-fin unbranched ray length	5.9	10.4	8.4	1.1
Body depth at dorsal-fin origin	14.4	19.3	17.1	1.6
Body width at dorsal-fin origin	26.3	32.8	29.8	1.9
Caudal peduncle depth	28.1	35.9	32.4	2.3
Caudal peduncle length	9.7	12.8	10.6	0.7
Cleithral width	31.6	35.8	33.3	1.3
Dorsal fin to adipose fin distance	12.1	18.2	15.0	1.9
Dorsal-fin base length	18.6	24.7	21.2	1.8
Dorsal-fin spine length	21.5	26.5	23.9	1.4
Head length	32.7	39.6	35.5	2.4
Interbranchial distance	16.2	20.8	18.4	1.4
Lower caudal-fin ray length	24.1	32.5	29.1	2.2
Pectoral-fin spine length	27.6	32.8	30.1	1.9
Pectoral fin to pelvic fin distance	21.2	25.7	24.0	1.3
Pelvic-fin unbranched ray length	21.7	27.8	24.0	1.6
Predorsal length	39.8	49.2	45.2	2.8
Supracleithral width	26.5	33.4	29.3	2.2
Upper caudal fin ray length	19.9	24.7	22.2	1.2
Percent of head length
Head depth at opercle	39.8	48.8	44.8	2.4
Internostril distance	14.8	21.4	17.7	1.8
Interorbital distance	35.6	44.2	39.3	2.5
Mandibulary ramus	12.9	19.9	15.9	2.1
Snout tip to ventral branchial opening	61.5	71.2	66.4	3.2
Orbital diameter	13.0	20.2	16.2	2.0
Snout length	53.6	62.9	58.5	2.6
Count			Mode
Premaxillary teeth	34	57	40
Dentary teeth	33	53	41
Plates in dorsal lateral series	20	22	21
Plates in median lateral series	22	24	23

TABLE 4 | Morphometric data of Ancistrus taunayi and A. multispinis. n = number of specimens; SD = Standard deviation.

		A. taunayi n = 18			A. multispinnis n = 11
	Min	Max	Mean	SD	Min	Max	Mean	SD
Standard length (mm)	48.3	100.9	74.4	–	45.5	112.5	83.6	–
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

TABLE 5 | Genetic distance between sequences of Ancistrus species from Rio Grande do Sul, conducted using the Kimura 2-parameter model with rate variation among sites modeled with a gamma distribution.

		1	2	3	4	5	6	7
1	A. aff. brevipinnis GravataÍ MCP 54885
2	A. aff. brevipinnis Sinos MCP 54882	0.003
3	A. brevipinnis Camaquã MCP 54895	0.027	0.030
4	A. brevipinnis Camaquã MCP 54896	0.029	0.032	0.005
5	A. brevipinnis Camaquã MCP 54896	0.029	0.032	0.005	0.000
6	A. megacanthus VacacaÍ MCP 54883	0.027	0.030	0.018	0.017	0.017
7	A. taunayi Santa Maria MCP 43914	0.023	0.027	0.022	0.023	0.023	0.025
8	A. multispinis Maquiné UFRGS 18448	0.019	0.022	0.020	0.020	0.020	0.015	0.018