Pseudolithoxus nicoi can be diagnosed by color pattern from most Pseudolithoxus: charcoal gray to black with white spots and a white band in the caudal fin. Pseudolithoxus nicoi differs from P. anthrax by the presence of a white band at the edge of the caudal fin.  Pseudolithoxus nicoi differs from Lasiancistrus sp. (see Discussion) by a greater dorsal base length to caudal depth ratio (3.2 - 3.5 vs. 2.1 - 2.2) and by having 5 anal-fin rays (vs. 4).

Body very dorsoventrally flattened with both ventral- and dorsal-surface flat.  Pectoral fins very elongate, pectoral-fin spine reaching anal fin in adults (only to anus in juveniles); very long, flexible odontodes present anterodistally on pectoral-fin spine.  Dorsal-fin spine weak; dorsal-fin spinelet supporting odontodes, v-shaped.  Dorsal fin short, folded dorsal fin not reaching median, unpaired preadipose plate.  Caudal fin weakly forked, lower lobe longer than upper.  Eyes mostly dorsal.  3 rows of plates on caudal peduncle.  Pterotic-supracleithrum bordered posteriorly at lateral line by small naked area ventrally and small plate dorsally.  Abdomen without plates.  Cheek odontodes hypertrophied, numerous, and set on evertible plates; odontodes fold into groove underneath opercle when relaxed.  Opercle studded with moderately elongate, stout odontodes along the ventral margin.  Cheek plates and opercle never with thin, whiskerlike odontodes.  Edge of snout anterior to evertible cheek plates with numerous hypertrophied odontodes.

Dorsal II 7, pectoral I 6, pelvic I 5, anal I 5 (anal-fin spine about half length of first branched ray).  Teeth long and slender with large lateral and small mesial cusp; teeth 52-80 (54-63) per jaw ramus; tooth number tends to increase with standard length.  Lateral line plates 23-25 (25); dorsal plates 6-7 (7); interdorsal plates 5-7 (6); adipose-caudal plates 7-8 (8); folded dorsal-fin plates 11-12 (12); and postanal plates 11-12 (12).

Color in alcohol charcoal gray to black, with faint, small, sparse light spots on head, fin rays, fin spines, and body.  Fish occasionally without spots.  Fins not banded.  Five faint dorsal saddles often visible, first anterior to dorsal fin, second beginning at level of second dorsal-fin ray, third below and slightly beyond posterior two rays of dorsal fin, fourth between dorsal and adipose fins, and fifth below and slightly beyond the adipose-fin membrane.  Abdomen slightly lighter than side, occasionally with light spots.  Ventral surface posterior to pelvic girdle colored as side.  A white band always present at the edge of caudal fin; a white band occasionally present at edge of dorsal fin.

Found in the Río Casiquiare and upper Río Negro in Estado Amazonas, Venezuela.

Named for Leo Nico of the United States Biological Service in appreciation of the fact that he collected most of the known specimens of this species.

Holotype.  MCNG 37033, 114.3 mm SL; Venezuela, Estado Amazonas, Departmento Río Negro, Río Manipitare (Río Siapa drainage), from about 5 to 8 km upstream from confluence with Río Siapa, L. Nico, S. Walsh, K. Winemiller, and A. Arrington, 16 January 1998.

Paratypes.  All collections Venezuela, Estado Amazonas.  MCNG 12441, 1, 112.4 mm SL, Departmento Río Negro, Río Negro en San Carlos, 01°55íN 67°04íW, L. Nico, 22 April 1985. - MCNG 12149, 1, 105.5 mm SL, Departmento Casiquiare, Río Casiquiare (Río Negro drainage), a lagoon adjacent to an area approximately 15 river kilometers above the mouth, 01°58íN 66°55íW, L. Nico, E. Conde, R. Stergios, G. Aymand, & P. Cardozo, 14 April 1985. - MCNG 12290, 1, 71.2 mm SL, Departmento Río Negro, Río Emoni (Río Siapa drainage), approximately 2 river km above the mouth with Río Siapa, 01°58íN 66°55í W, L. Nico, E. Conde, R. Stergios, G. Aymand, & P. Cardozo, 14 April 1985. - MBUCV V-29125, 1, 98.6 mm SL, collected with holotype. - ANSP 177766, 1, 67.4 mm SL; MCNG 37034, 2, 32.3 mm SL, Río Siapa (Río Casiquiare drainage), at campsite near Laguna Cumicapi between Río Emoni and Río Manipitare, K. Winemiller, D. Jepsen, A. Arrington, et al. 16 January 1998. - MCNG 37035, 1, 37.0 mm SL, Río Pasimoni (Río Casiquiare drainage), at Piedra Arapacoa - right descending bank, 01°52.5íN 66°35.2íW, L. Nico, D. Jepsen, S. Walsh, & A. Barbarino, 20 January 1998. - MCNG 37036 (1, 48.3 mm SL), Río Emoni (Río Siapa drainage), approximately 1-2 km upstream from confluence with Río Siapa, ~02°07íN ~66°20í W, L. Nico, S. Walsh, G. Yavinape, & D. Payema, 19 January 1998. - MBUCV V-27916, 1, 60.5 mm SL; MCNG 37037, 1, 47.5 mm SL, Río Emoni (Río Siapa drainage), from near mouth to approx. 2-3 km upstream, S. Walsh, L. Nico, et al. 17 January 1999. - MCNG 37038, 1, 60.3 mm SL, Río Manipitare (Río Siapa drainage), ca. 8 km upstream from its mouth, K. Winemiller, L. Nico, S. Walsh, & A. Barbarino, 16 January 1998. - AUM 28355, 1, 77.0 mm SL; MCNG 37039, 2, 45.5 mm SL, Río Manipitare (Río Siapa drainage), approx. 4-5 km upstream from mouth, S. Walsh & D. Jepsen, 15 January 1998.

LITERATURE CITED

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