Chaetostoma Tschudi, 1846


Chaetostoma milesi, photo by J.W. Armbruster


Chaetostoma platyrhynchus, photo by J.W. Armbruster
TAXA LIST


Chaetostoma used to be easy: they were the loricariids without plates on the snout and without tentacles, but I found that Cordylancistrus platyrhynchus was actually a part of Chaetostoma, but that it does have plates along the snout. This is the danger of using a single characteristic to diagnose a group. Most major clades will have one to several successive groups leading up to it that lack the advanced characteristic. In fact, there are a couple of other species of Cordylancistrus that appear to be a step down from Ch. platyrhynchus and share with Chaetostoma the derived presence of enlarged papillae behind the dentary while the type species of Cordylancistrus (Co. torbesensis) appears to be sister to all other members of the Chaetostoma group. The choice would be to describe several new genera, all of which would be monotypic and poorly diagnosed, expand Chaetostoma to include some, but not all species of the Chaetostoma group with plates along the snout, or recognize the very well diagnosed Chaetostoma group as a single genus. I think that the latter is much more scientifically sound. Subgenera could be erected for some of the oddities as their recognition usually does not require as great of vigor, and species can be moved between subgenera without changing the binomial.

Chaetostoma is the second largest genus of the Ancistrini with 44 described, accepted species. The following is an excerpt from Armbruster (1997).



SPECIES


DIAGNOSIS

Chaetostoma is not diagnosed by any unique characteristic.  Characteristics considered synapomorphic for Chaetostoma are: the loss of the suture between the hyomandibula and the pterotic-supracleithrum, a wide quadrate, and only slight contact between the suprapreopercle and IO6.



DESCRIPTION

Most species of Chaetostoma are small fishes with small eyes and large jaws.  All species lack plates on the abdomen, and all but one species lacks plates on the margin of the snout.  Color pattern is generally gray to black, and species may be adorned with mottling or spots, sometimes with egg-yellow spots at the tips of the caudal fin or a white to yellow band on the posterior border of the caudal fin.  Caudal fin varies from slightly emarginate to straight, angling posteroventrally.  Four or more predorsal plates with the nuchal plate covered by other plates so that it appears absent.  The dorsal fin spinelet is present and triangular, but it is covered in skin and appears absent because it generally does not support odontodes.  Five rows of plates on the caudal peduncle.  The lower jaws often have papillae that are slightly larger than the main buccal papilla situated just behind the teeth.  Some species have a black, fleshy keel behind the supraoccipital.  Dorsal surface of head between the eyes is covered in thick skin, and odontodes are either absent or barely break the surface of the skin.  The cheek odontodes are generally weakly developed.

Males of some species develop large, fleshy flaps on the pectoral fin rays (Ceas, pers. comm.).  Males of C. platyrhynchus also develop fleshy, fimbriate folds along the pelvic-fin spine and anterior rays



COMPARISONS

Most species of Chaetostoma are readily recognized from all other Ancistrini except Ancistrus by the absence of plates on the anterior margin of the snout.  Chaetostoma differs from Ancistrus by the lack of fleshy tentacles on the snout.  Chaetostoma platyrhynchus does have plates on the snout and can be separated from all other loricariids (except other Chaetostoma group members) by the lack of odontodes on the nuchal plate and dorsal-fin spinelet.  It differs from Cordylancistrus, Dolichancistrus, and Leptoancistrus by having few, short odontodes on the evertible cheek plates (vs. numerous and long).



DISTRIBUTION

Chaetostoma is found on both sides of the Andes from Bolivia to Panama including the arm of the Andes that extends along the Caribbean in Venezuela.  Two species, C. vasquezi and C. jegui, are found in the Tipuis of the Guyana Shield in southern Venezuela and northern Brazil.


ECOLOGY

Species of Chaetostoma typically inhabit mountainous streams from small creeks to medium-sized rivers.  They are often found in the fastest current.  Males defend nests under flat rocks where the eggs are laid in a single layer on the roof of the nest (Page et al., 1992).



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.

Page, L.M., G.B. Mottesi, M.E. Retzer, P.A. Ceas, and D.C. Taphorn. 1993. Spawning habitat and larval development of Chaetostoma stannii (Loricariidae) from Rio Crucito, Venezuela. Ichthyol. Explor. Freshwaters 4:93-95.


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