Exastilithoxus Isbrücker and Nijssen, 1979


Exastilithoxus fimbriatus, photo by J.W. Armbruster

TAXA LIST

Exastilithoxus (along with its sister, Lithoxus) are fairly unique among loricariids in that they subsist entirely on a diet of insect larvae.  Two species, E. fimbriatus and E. hoedemani, are described.  The following is an excerpt from Armbruster (1997).

SPECIES
DIAGNOSIS

Exastilithoxus is not diagnosed by any unique characteristic.  Characteristics considered synapomorphic for Exastilithoxus 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.


DESCRIPTION

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.


COMPARISONS

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


ECOLOGY

Only insect larvae were found in the gut of the one Exastilithoxus examined.


DISTRIBUTION

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.


LITERATURE CITED

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, a new species of mailed catfish from rio Marauiá, est. Amazonas, Brazil (Pisces, Siluriformes, Loricariidae). Spixiana 8:221-229.


If you have any comments or questions regardng this site, please contact Jon Armbruster at armbrjw@mail.auburn.edu