Leptoancistrus canensis, photo by K.S. Cummings
Leptoancistrus is not diagnosed by any unique characteristic. Characteristics considered synapomorphic for Leptoancistrus are: reduction in the width of the fifth ceratobranchial such that it is bar-shaped, an opercle that passes to the anterodorsal corner of the quadrate, seven or more infraorbital plates, two large, perforated hemal arches in front of the centrum in contact with the first anal fin pterygiophore, loss of the adipose fin , three or more median preadipose plates, loss of the anal fin rays (2 pterygiophores still present), and a postdorsal ridge of raised, median plates.
Leptoancistrus is a small loricariid lacking adipose and anal fins. The color pattern is dark brown and mottled with the fins spotted and the ventral surface white. Abdomen naked. Caudal fin straight, angled posteroventrally. Four or more predorsal plates with the nuchal plate covered by plates. The dorsal fin spinelet is covered with skin as in the rest of the Chaetostoma group. Five rows of plates on the caudal peduncle. The adipose fin is absent and replaced by a postdorsal ridge composed of several median, unpaired plates. The dorsal odontodes of the cheek mass are very long.
Differs from all loricariids except some Chaetostoma by the absence of an anal fin. Differs from Chaetostoma without an anal fin by having plates on the snout.
Known only from Panama and northern Colombia.
Leptoancistrus is a high-montane fish occurring sympatrically with Astroblepus. Of the loricariids examined by Gee (1976), Leptoancistrus was the only one that did not breathe air.
Armbruster, J.W. 1997. Phylogenetic relationships of the sucker-mouth armored catfishes (Loricariidae) with particular emphasis on the Ancistrinae, Hypostominae, and Neoplecostominae. Unpubl. Ph.D. dissertation. University of Illinois, Urbana-Champaign. 409 pp.
Gee, J.H. 1976. Buoyancy and aerial respiration: factors influencing the evolution of reduced swim-bladder volume of some Central American catfishes (Trichomycteridae, Callichthyidae, Loricariidae, Astroblepidae). Can. J. Zool. 54:1030?1037.