Lithoxus lithoides, photo above by J.W. Armbruster and below by M.H. Sabaj
Paralithoxus Boeseman, 1982. Originally
described as a subgenus, but elevated to generic rank by Isbrücker
and Nijssen (1985), and subsequently returned to the synonymy of Lithoxus
and is no longer recognized as a valid subgenus by Nijssen and Isbrücker
Lithoxus is diagnosed by three unique characteristics: a process on the preoperculo-hyomandibular ridge, a ventrally oriented, spoon-shaped anterior process of the metapterygoid, and an enlarged, thin-walled stomach from which the intestine exits dorsally. Other characteristics considered synapomorphic for Lithoxus are: a reduction in the width of the fifth ceratobranchial such that it is bar-shaped, loss of the accessory process of the first epibranchial, loss of the shelf of the parasphenoid, an expanded distal end of the expanded rib of the sixth vertebral centrum, an abductor fossa of the pectoral girdle that is almost flat anteromesially, and a reversal to thin anterolateral processes of the pelvic basipterygium.
Lithoxus contains some of the most dorsoventrally flattened fishes in the world. Color is typically slate gray to tan with a few lighter markings on the body and occasionally bands in the pectoral and caudal fins. Ventral surface ranges from white to slightly lighter than the sides. Abdomen naked. Caudal fin slightly forked. Four or more predorsal plates. Three rows of plates on the caudal peduncle. The lower lip is large and round as in Exastilithoxus with the edge sometimes frilled, but not with the barbels seen in Exastilithoxus. The jaws are reduced with very few teeth (less than six per premaxilla). The premaxillary teeth are longer than the dentary teeth.
Breeding males develop extremely long odontodes
on the leading edge of the pectoral fin spine. The expanded stomach
is slightly larger in males.
Lithoxus can be separated from all other Ancistrini except Leporacanthicus
and Exastilithoxusby having a round (vs. oval) lower lip. Lithoxus
be separated from Leporacanthicus by lacking tentacles on the upper
lip and by having 3 (vs. 5) rows of plates on the caudal peduncle, and
from Exastilithoxus by lacking short fimbriae along the lower lip
(the posterior rim of the lower lip is smooth in Lithoxus).
Lithoxus is said to inhabit both rivulets (Boeseman, 1982) and medium-sized creeks (Eigenmann, 1912). We collected some of Lithoxus
from riffle on the main-stem Essequibo River in Guyana. These peripheral habitats are among the first parts of the river to dry and the respiratory stomach may have evolved to handle this periodic drying. The large size and small number of eggs suggest that parental care is well developed, but nothing is known of the breeding habits of Lithoxus. The
flattened morphology suggests that Lithoxus lives under rocks.
Known from throughout the Guyanas and also in the Rio Negro of Brazil. We recently discovered a new species in the upper Rio 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.
Armbruster, J.W. 1998. Modifications of the digestive tract for holding air in loricariid and scoloplacid catfishes. Copeia 1998:663-675.
Boeseman, M. 1982. The South American mailed catfish genus Lithoxus Eigenmann, 1910, with the description of three new species from Surinam and French Guyana and records of related species (Siluriformes, Loricariidae). Proc. Konink. Nederl. Akad. Wetens., ser. C 85:41?58.
Eigenmann, C.H. 1912. The freshwater fishes of British Guiana, including a study of the ecological grouping of species and the relation of the fauna of the plateau to that of the lowlands. Mem. Carnegie Mus., 5:1?578.
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.
Nijssen, H. and I.J.H. Isbrücker. 1990. Lithoxus stocki, a
species new to science of ancistrin loricariid catfish from the Maroni
River drainage, with a comparison of the primary type specimens of six
species of Lithoxus (syn. Paralithoxus) (Pisces, Siluriformes,
Loricariidae). Bijd. tot Dierk. 60:327-333.