Pseudolithoxus dumus is diagnosed from
Pseudolithoxus by the presence of a light body color with
large, black spots at least anteriorly (spots may combine posteriorly to
form bars). P. dumus can also be separated from all but P. tigris
by the presence of light orange to cream-colored spots at the tip of the
dorsal- and caudal-fin spines.
Body very dorsoventrally flattened with both ventral and dorsal surface flat. Extremely hypertrophied 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. Edge of snout anterior to evertible cheek plates with numerous hypertrophied odontodes. All odontodes on opercle moderately elongated and stout. Cheek plates and opercle never with thin, whiskerlike odontodes. Pectoral-fin spine moderately elongated, reaching anus.
Dorsal II 7; pectoral fin I 6; pelvic fin I 5; anal fin I 5 (anal-fin spine about half first branched ray). Teeth long and slender with large lateral and small mesial cusp; teeth 37-79 (58-67) per jaw ramus; tooth number tends to increase with standard length. Lateral line plates 24-25 (25); dorsal plates 6-9 (7); interdorsal plates 6-7 (6); adipose-caudal plates 6-7 (6); folded dorsal-fin plates 11-14 (12); and postanal plates 11-13 (12).
Color in alcohol consists of gray-brown base color and fairly large,
black spots on head and body to below middle of dorsal fin. Spots
fade towards caudal fin, spots either absent on caudal peduncle, present
only along midline, or combine to form thin, often wavy black bars (see
Comments. Four faint saddles occasionally visible on back, first
below anterior of dorsal fin, second below posterior of dorsal fin, third
between dorsal and adipose fins, and fourth under adipose-fin membrane.
Fin rays and spines spotted so that fins appear banded (caudal fin occasionally
entirely gray). Dorsal- and caudal-fin spines tipped with light orange
or cream-color spots. Adipose-fin membrane dark. Abdomen just
slightly lighter than side.
Known from the upper Río Orinoco and tributaries of southern Venezuela from about Puerto Ayacucho to the Río Casiquiare.
From the Latin dumus for thorn-bush, in
reference to the well developed odontodes on the pectoral-fin spines and
snout; treated as a noun in apposition.
Holotype. MBUCV V-17544, 86.8 mm SL, Venezuela, Estado Amazonas; Río Orinoco, backwater behind sand playa circa 0.5 hr upstream from Isla Temblador, 03°04íN 66°28íW, B. Chernoff, H. Lopez, W. G. Saul, J. Fernandez, O. Castillo, M. E. Antonio, J. Moreno, 10 March 1987.
Paratypes. All collections Venezuela, Estado Amazonas. ANSP 162403, 1, 70.6 mm SL; MBUCV V-17543, 1, 79.9 mm SL, collected with holotype. - MCNG 25796, 1, 58.4 mm SL, Departmento Atabapo, Río Ocamo at Raudal Arata, 03°08íN 64°34íW, L. Nico and J. Castillo, 24 January 1990. - ANSP-162160, 1, 99.1 mm SL, Río Orinoco, creek between the island and the beach, just downstream from Quiritare, (Quiritare is at 03°02íN 66°04íW), B. Chernoff, H. Lopez, J. Fernandez, and W. G. Saul, 11 March 1987.
Non-types. All collections Estado Amazonas, Venezuela. FMNH
106027, 2, 81.9 - 83.5 mm SL; MBUCV V-23082, 1, 41.9 mm SL, Río
Ventuari, S side of river ca 0.5 hr. (ca. 12 km) above mouth in Río
Orinoco, Laguna Pavón, 04°04íN 66°56íW, B. Chernoff, A.
& D. Machado, and J. Wheeler, 24 January 1991. - ANSP 160769, 1, 101.2
mm SL; MBUCV V-16867,1, 76.1 mm SL, Morichal, 26 km from Puerto Ayacucho
on road to Caicara, B. Chernoff, B. Saul, and R. Royero, 15 November 1985.
- MBUCV V-14649, 1, 89.6 mm SL, Río Cataniapo, Raudal Yawi 5 river
km upstream from La Reforma, 28 December 1984.
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