Lasiancistrus Regan, 1904

Armbruster, Jonathan W., 2005, The loricariid catfish genus Lasiancistrus (Siluriformes) with descriptions of two new species, Neotropical Ichthyology 3 (4), pp. 549-569 : 550-552

Lasiancistrus Regan, 1904

Type Species. Chaetostomus heteracanthus Günther, 1869: 425 , Figs. 3-4 .

Diagnosis. Lasiancistrus is diagnosed by two unique synapomorphies from Armbruster (2004): presence of a posteriorly directed strut of the pterotic leading from the anterior process of the pterotic to the main body of the pterotic, which causes the dilatator operculi chamber to be open posteriorly (114: 1; Fig. 1 ; originally described by Schaefer, 1986) and presence of whiskerlike odontodes on the cheek (186: 1, Fig. 2 ). Lasiancistrus is also diagnosed by the following homoplastic synapomorphies: three branchiostegals (5:1), presence of a posteromedial invagination of the fifth ceratobranchial (11:1), presence of a ventral process on the quadrate for articulation with the canal plate (65:1), infraorbital six forming the entire ventral border of the orbit (89:1), loss of a deep pouch posteroventrally on the lateral ethmoid (98:0), loss of contact of the sphenotic and infraorbital six (117:1), and distal margin of rib of sixth vertebra flared distally so that the tip is much wider than the shaft (128:1).

by lacking keels on the lateral plates; from Exastilithoxus and Lithoxus by having greater than 30 teeth per jaw ramus (vs. less than 10) and by having oval lips (vs. round); from Neblinichthys by lacking hypertrophied odontodes on top of the head in nuptial males; and from Pseudolithoxus by lacking long, bristle-like odontodes on the leading edge of the pectoral-fin spine.

Description. Member of Ancistrini as diagnosed by Armbruster (2004). Medium-sized loricariids, largest specimen 190.4 mm SL. Body strongly dorsoventrally compressed and moderately wide. Head and nape gently sloped to insertion of dorsal fin. Dorsal profile very slightly sloped ventrally to dorsal procurrent caudal-fin spines, then rising slightly to caudal fin. Ventral profile flat to caudal fin. Supraorbital ridge almost absent with interorbital space slightly concave, almost flat. Supraorbital ridge continues as slightly higher, rounded ridge from anterior of orbit to slightly anteroventral of anterior nare. Mesethmoid raised slightly above lateral surface of snout to form slight ridge. Head contours smooth. Eyes small to medium.

Keels absent. All plates slightly convex medially to produce cylindrical body. Mid-dorsal and mid-ventral plate rows incomplete, generally ending below adipose fin; three rows of plates on caudal peduncle. Abdomen either naked, with

Adult Lasiancistrus can be separated from all other loricariids by the presence of whiskerlike odontodes on the cheek. In addition, Lasiancistrus can be separated from all other loricariids except members of the Pterygoplichthyini and Ancistrini by the presence of evertible cheek odontodes; from the Pterygoplichthyini by having three rows of plates on the caudal peduncle (vs. five) and a modified, bar-shaped opercle (vs. a triangular opercle); from all except Ancistrus , Dekeyseria , Exastilithoxus , Lithoxus , Neblinichthys , and Pseudolithoxus of the Ancistrini by having three rows of plates on the caudal peduncle (vs. five, rarely four); from all but Ancistrus by having nuptial males with tentacules on the pectoral-fin spines longer than their associated odontodes; from Ancistrus by having plates along the edge of the snout (vs. snout plates absent) and by maximally having transluscent tentacules on the snout that have odontodes associated with them (vs. larger tentacles without associated odontodes colored the same as the head; even female and juvenile Ancistrus have some tentacles along the snout margin); from Dekeyseria few small plates near insertion of pectoral-fin spine, or with very small, embedded plates from pectoral girdle to anterior of pelvic girdle. First anal-fin pterygiophore not exposed to form platelike structure. 21-25 (mode = 24) plates in median series.

Frontals, infraorbitals, nasals, opercles, pterotics, sphenotics, and supraoccipital supporting odontodes. Opercular odontodes occasionally moderately hypertrophied, thick, and sharp; whiskerlike odontodes rarely present on opercle. Whiskerlike odontodes present in evertible cheek mass and occasionally at anterolateral corner of snout; 0-35 (mode = 13, N=152) whiskerlike odontodes in evertible cheek mass with number of whiskerlike odontodes increasing with size; 12-76 (mode = 25, N=159) total hypertrophied odontodes in cheek mass. Cheek plates evertible to approximately 90° from head, hypertrophied cheek odontodes folded under opercle when relaxed. Odontodes on tip of pectoral-fin spine slightly hypertrophied. Odontodes on lateral plates not enlarged to form keels.

Dorsal fin not reaching preadipose plate when adpressed; dorsal-fin spine not elongate, edge of dorsal fin straight. Dorsal-fin spinelet V-shaped, dorsal-fin spine lock functional. Dorsal fin II,7 (one of 280 individuals II,6). Adipose fin with one preadipose plate and moderately long spine. Caudal fin slightly emarginate to forked, lower lobe longer than upper, i,14,i (one of 286 individuals i,11,i, two i,12,i, and four i,13,i) with three to five (mode five, N=157) dorsal procurrent caudal-fin rays and three to five (mode 4, N=157) ventral procurrent caudal-fin rays. Anal fin short with unbranched ray weak and usually about three quarters length of first branched ray.Anal fin i,5 (one of 307 specimens i,1, five i,4, and one i,6), Pectoral-fin spine reaching slightly posterior to insertion of pelvic fin when adpressed ventral to pelvic fin. Pectoral fin I,6 (three of 307 individuals I,5). Pelvic fin reaching to posterior of anal-fin when adpressed. Pelvic fin i,5 (N=307).

Dorsal flap of iris present. Flap between anterior and posterior nares short. Lips wide, fairly thin. Upper lip with small, round papillae. Lower lip with medium-sized papillae anteriorly and smaller ones posteriorly. Maxillary barbels very short, not reaching behind lower lip, occasionally completely adnate. Buccal papilla small. Jaws moderately wide, dentaries forming very oblique angle; premaxillaries forming a very shallow arc with an overall angle just slightly less than 180°. Teeth with fairly long, narrow cusps; lateral cusp approximately half-length of medial cusp, stalks of teeth long; 39-101 dentary teeth (mode = 74, N=137) and 29-97 premaxillary teeth (mode = 60, N=141).

Sexual dimorphism. Snout of nuptial males almost square (vs. rounded in females and juveniles). Adult males of most species (except Lasiancistrus tentaculatus ) with whiskerlike odontodes at anterolateral corner of snout ( Fig. 2a ); males of L. tentaculatus with tentacules instead of whiskerlike odontodes along anterior margin of snout ( Fig. 2b ). Nuptial males with tentacules longer than their associated odontodes on the pectoral-fin spine ( Sabaj et al., 1999).

Range. Found throughout the Amazon River basin, the upper and middle of the Orinoco River basin, the Rupununi River basin ( Essequibo River drainage), the Lake Maracaibo drainage, and drainages west of the Andes in Colombia and Panamá to the Bayano River ( Fig. 3 ).

Key to the Species of Lasiancistrus :

1. Dorsal fin with either white spots in the dorsal fin or dorsal fin plain. Body typically with light spots or entirely dark ................................................................................................ 2

1’. Dorsal fin with black spots. Body with dark markings, light markings (if present) usually present as blotches or thick lines (except in río Bayano population in Panamá), body never completely dark ........................................................ 3

2. Body and fins with small white spots less than half the diameter of the plates (although spots may be faded). Plates entirely dark or with small spots ..... L. schomburgkii

2’. Body and paired fins with large white spots almost the same size as the plates, dorsal fin without spots. Plates outlined in black ................................................. L. saetiger

3’. Abdomen without plates ...................................................... 4

3. Abdomen with plates in at least a small patch medial to the insertion of the pectoral-fin spines .................................... 5

4. Nuptial males with whiskerlike odontodes at the corners of the snout ( Fig. 4 , see also Fig. 2a ). Caudal fin emarginate ............................................................................ L. caucanus

4’. Nuptial males with tentacules along the anterior margin of the snout ( Fig. 2b ). Caudal fin forked ........... L. tentaculatus

5. Abdomen with plates underneath entire pectoral girdle and on abdomen ............................................. L. heteracanthus

5’. Abdomen with only a couple of plates medial to insertion of pectoral-fin spines ................................... L. guacharote

Figures

Fig. 3. Range of species of Lasiancistrus. Open symbols are type localities except for in L. heteracanthus where the type locality is not specific. Triangles = L. schomburgkii, squares = L. caucanus, upside down triangles = L. guacharote, diamonds = L. heteracanthus, cross = L. saetiger, and circles = L. tentaculatus. The following are type localities for species in synonymy that have good locality information: 1. L. castelnaui (locality approximate), 2. L. guapore, 3. L. maracaiboensis, 4. L. mayoloi, 5. L. planiceps, 6. L. scolymus, 7. L. volcanensis.

Fig. 4. Dorsal, lateral, and ventral views and inset of extended caudal fin of Lasiancistrus caucanus, SIUC 34914, 92.3 mm SL.

Fig. 1. Pterotic, right side, ventral view: a. Ancistrus pirareta, UMMZ 206085, b. Lasiancistrus guacharote, INHS 60465. Scale bars = 1 mm. Shaded area is cartilage. APT = anterior process of the pterotics, PR = prootic, PT = pterotics, and PTS = pterotics strut (forms over the open dilatator operculi chamber).

Fig. 2. Heads, dorsal view showing whiskerlike odontodes on cheek (a and b), whiskerlike odontodes on snout (a) and tentacules on snout (b) a. Lasiancistrus guacharote, ANSP 128695, 123.4 mm SL, b. Lasiancistrus tentaculatus, INHS 28650,105.5mmSL.