Pseudolithoxus anthrax, photo by M.H. Sabaj
Pseudolithoxus dumus, photo by M.H. Sabaj
Pseudolithoxus tigris, photo by M.H. Sabaj
With approximately 645 valid species, the Loricariidae is the largest family of catfishes in the world (Isbrücker, 1980; pers. obs.). Recent expeditions into areas that hitherto have been virtually unexplored have yielded many examples of undescribed species and genera of the Loricariidae. Amazonas, the southernmost state of Venezuela, has been one such locality. While examining fishes collected in Amazonas, we became aware of a monophyletic group of species of the subfamily Ancistrinae that are characterized by evertible cheek plates, a very dorsoventrally flattened body, extremely hypertrophied odontodes (integumentary teeth) on elongated pectoral spines and along the snout margin, and 3 rows of plates on the caudal peduncle. In addition, it appears as if females as well as males develop hypertrophied snout and pectoral-fin odontodes, traits normally restricted to nuptial males. Comparison of these species with types and/or original descriptions of other loricariids has led us to the conclusion that the species are undescribed.
The four new species described herein are most similar to Lasiancistrus Regan. A review of some type specimens and all original species descriptions of Lasiancistrus reveals that Lasiancistrus (sensu Isbrücker, 1980 and Heitmans et al., 1982) is a polyphyletic taxon. At present, there are no published studies that diagnose Lasiancistrus; however, the unpublished study of Armbruster (1997) suggests that Lasiancistrus be restricted to those species that can be superficially recognized by the presence of long, narrow odontodes on the evertible cheek plates that look like whiskers. Sabaj et al. (1999) suggest a close relationship of Lasiancistrus sensu stricto with Ancistrus based on the shared derived presence of large tentacles on the snouts of males (in Lasiancistrus, the tentacles are not as large as those of Ancistrus and they are associated with hypertrophied odontodes). The four new species lack whiskerlike odontodes and large tentacles; however, until the genera of Ancistrinae can be better diagnosed and a phylogeny becomes available, it is most conservative to describe the new species in Lasiancistrus (The genus has since been described as Pseudolithoxus).
P. anthrax, P. nicoi, P. dumus and
tigris are described and compared, and some of the biogeographical
aspects of their evolution are discussed.
DIAGNOSIS OF Pseudolithoxus
Pseudolithoxus differs from
sensu stricto by lacking thin, whiskerlike odontodes on the evertible cheek
plates and from all other ancistrines except Ancistrus, Dekeyseria,
Exastilithoxus, Lithoxus, and Neblinichthys by having 3 rows
of plates on the caudal peduncle (vs. 4-5; all described Lasiancistrus
that do not have whiskerlike odontodes have 4-5 rows of plates on the caudal
peduncle). The L. anthrax species group further differs from
by having plates along the anterior margin of the snout (vs. anterior part
of snout naked) and by lacking tentacles on the snout; from Dekeyseria
by lacking well-keeled lateral plates; from Exastilithoxus by lacking
frimbriae on the lower lip; from Exastilithoxus and Lithoxus
by having much greater than 20 teeth per jaw ramus; and from Neblinichthys
by lacking elongate odontodes on the top of the snout of breeding males.
The key below serves to separate the species of Pseudolithoxus and
a similar, sympatric species referred to as Lasiancistrus sp. (see
KEY TO THE SPECIES OF THE SPECIES OF Pseudolithoxus
|1a.||Body black, usually with white spots (the white spots may be faded and indistinct in preserved specimens). Dark bands absent on caudal fin.||2|
|1b.||Body with brown and tan bars or gray-brown with black spots. Dark bands usually present on caudal fin.||4|
|2a.||Caudal fin with white band at distal margin.||P. nicoi|
|2b.||Caudal fin without white band at distal margin.||3|
|3a.||Base of dorsal-fin length to caudal depth ratio 2.1-2.2. 5 anal-fin rays (rarely 4).||P. anthrax|
|3b.||Base of dorsal-fin length to caudal depth ratio 2.9-3.5. 4 anal-fin rays.||Lasiancistrus sp.
|4a.||Color pattern consisting of black spots on head and anterior part of body.||P. dumus|
|4b.||Color pattern consisting of brown and tan bars on head and anterior part of body.||P. tigris|
Most species are restricted to Amazonas, Venezuela in the upper Río Orinoco and upper Río Negro and their tributaries. One species (the one on the top above) is also found in the Ríos Caura and Aro of Bolivar state, Venezuela.
The range of P. anthrax versus P. nicoi is very interesting biogeographically. Due to their very similar color patterns, L. anthrax and L. nicoi most likely represent sister taxa. As such, it is interesting to note that P. anthrax ranges throughout the upper Río Orinoco (as well as the Río Caura and Río Aro) with collections available almost to the Río Casiquiare. In contrast, P. nicoi is found in the Río Casiquiare and the upper Río Negro. The Río Casiquiare connects the Río Orinoco with the Río Negro. The distribution of the species suggests that the Río Negro and the Río Orinoco once were split, and the current connection between the two arose only recently.
We propose that the species described herein represent a monophyletic group based on the shared, derived presence of extremely hypertrophied, flexible odontodes on the pectoral-fin spines. Among potentially closely related ancistrines, only Lithoxus Eigenmann develops similar structures. Unfortunately, few specimens have been available for a detailed examination of the osteology of these species, and the authors disagree with the distribution of various character states among ancistrines. Therefore, we defer discussion of the osteology of these species to a later date. The presence of hypertrophied odontodes along the snout in both males and females is probably also a synapomorphy, but not enough specimens are available to determine if this trait is present in all species. Among ancistrines, only Pseudancistrus and Lithoxancistrus have hypertrophied odontodes along the snout in both males and females (hypertrophied snout odontodes are usually restricted to nuptial males when present). Based on the characters of Armbruster (1997), the Pseudolithoxus is not the sister group to Lithoxus, Pseudancistrus, or Lithoxancistrus.
During the course of this study, we have also found a species that resembles
anthrax and P. nicoi from Amazonas, Venezuela. The species
is referred to as Lasiancistrus sp. in the key above. Lasiancistrus
sp. is also black with white spots, but is not as strongly dorsoventrally
flattened as P. anthrax and P. nicoi, and it does not have
particularly elongate odontodes on the pectoral-fin spines. The body
shape is much more indicative of the shape of other species of Lasiancistrus;
however, Lasiancistrus sp. also lacks whiskerlike odontodes on the
cheek and tentacles on the snout. We do not describe Lasiancistrus
sp. here because it does not appear to be part of Pseudolithoxus,
and we have insufficient material.
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