Exastilithoxus fimbriatus, photo by J.W. Armbruster
Exastilithoxus is not diagnosed by any
unique characteristic. Characteristics considered synapomorphic for
are: greatly elongated first hypobranchials, a levator arcus palatini crest
that is angled such that it ends above the metapterygoid facet for articulation
with the lateral ethmoid, a short anterior process of the metapterygoid,
loss of plates between the opercle and pterotic-supracleithrum, loss of
plates between the suprapreopercle and the exposed opercle, seven infraorbital
plates, loss of the mesethmoid disk, eight to nine postdorsal vertebrae,
a reduced posterior process of the cleithrum, no fenestra in the pelvic
basipterygium, and a dorsal shift of the pectoral fin spine such that it
lies significantly above the pelvic fin spine.
Exastilithoxus is a small, cylindrical loricariid with a round lower lip adorned with fleshy barbels. Color pattern is generally mottled and dark brown with paler areas under and just posterior to the dorsal fin. The abdomen is white. Fins are mottled. Ventral surface of the caudal peduncle is colored as the sides, but slightly lighter. Abdomen naked. Caudal fin slightly forked with the lower lobe longer than the upper. Four or more predorsal plates. Three rows of plates on the caudal peduncle.
Exastilithoxus is very similar to Lithoxus with Lithoxus varying in form from almost Exastilithoxus-like to flat. Exastilithoxusis readily recognized from all other Hypostominae by the presence of fimbriae along the posterior margin of the lower lip; however, Lithoxus also has projections on th elower lip, but they are much smaller than in Exastilithoxus.
Exastilithoxus fimbriatus mouth showing fimbriae along lower lip and round lips, photo by J.W. Armbruster
Only insect larvae were found in the gut of the one Exastilithoxus examined.
One species described from the Río Kukenan (Río Caroni drainage; Kukenan is often spelled Coquenan) of southeastern Venezuela and the other from the Rio Maurauiá drainage (a stream draining the Cerro de la Neblina) of northern Brazil. There appears to be an undescribed species in the upper Orinoco.
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.
Isbrücker, I.J.H. and H. Nijssen. 1985. Exastilithoxus hoedemani,
new species of mailed catfish from rio Marauiá, est. Amazonas, Brazil
(Pisces, Siluriformes, Loricariidae). Spixiana 8:221-229.