Pseudolithoxus Isbrücker and Werner (2001)


Pseudolithoxus anthrax, photo by M.H. Sabaj

Pseudolithoxus dumus, photo by M.H. Sabaj

Pseudolithoxus tigris, photo by M.H. Sabaj

TAXA LIST

Armbruster and Provenzano (2000) described four new species of Lasiancistrus from southern Venezuela.   I find that the four species form a monophyletic sister group to Lasiancistrus + Ancistrus.  I had planned on describing this genus upon publication of a phylogeny that would prove that it is a distinct, monophyletic group; however, Isbrücker and Werner (in Isbrücker et al., 2001), using the data in Armbruster and Provenzano (2000) and doing little but translating our words into German, scooped me and gave this group the unfortunate name of Pseudolithoxus (I say unfortunate because the name means false Lithoxus, but the fishes are not closely related to Lithoxus and their morphology is only somewhat similar to Lithoxus - certainly the genus is much more like Lasiancistrus).  The new genus lacks whisker-like odontodes as well as other synapomorphies for Lasiancistrus such as 3 (vs. 4) branchiostegal rays, and an open dilatator operculi chamber. The reason why the genus was not described in Armbruster and Provenzano (2000) was becuase Provenzano and I disagreed as to whether it was a genus, the diagnosis at the time was poor (it still is, but at least a phylogeny backs it up), and no legitimate scientific journal would have accepted a description of the genus at that time. Being scooped isn't so bad, but being scooped with ones own words is not good science.  The following is an excerpt from Armbruster and Provenzano (2000)

SPECIES


INTRODUCTION

 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 P. tigris are described and compared, and some of the biogeographical aspects of their evolution are discussed.



DIAGNOSIS OF Pseudolithoxus

Pseudolithoxus  differs from Lasiancistrus 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 Ancistrus 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 Discussion).



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.
   (see Discussion)
   
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



DISTRIBUTION

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.

DISCUSSION

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 P. 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.



LITERATURE CITED

Armbruster, J.W. and F. Provenzano. 2000.  Four new species of the suckermouth armored catfish genus Lasiancistrus (Loricariidae: Ancistrinae). Ichthyological Exploration of Freshwaters 11:241-254.

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, Univ. Illinois, Urbana-Champaign, 409 pp.

Armbruster, J. W. 1998. Phylogenetic relationships of the suckermouth armored catfishes of the Rhinelepis group (Loricariidae: Hypostominae). Copeia 1998: 620-636.

Armbruster, J. W. & M. Hardman. 1999. Redescription of Pseudorinelepis genibarbis (Loricariidae: Hypostominae) with comments on behavior as it relates to air-holding. Ichthyol. Explor. Freshwaters, 10: 53-61.

Armbruster, J. W. & L. M. Page., 1996. Redescription of Aphanotorulus (Teleostei: Loricariidae) with description of one new species, A. ammophilus, from the Río Orinoco basin. Copeia, 1996: 379-389.

Boeseman, M. 1968. The genus Hypostomus Lacépède, 1803, and its Surinam representatives (Siluriformes, Loricariidae). Zool. Verhand., 99: 1-89.

Heitmans, W. R. B., H. Nijssen, & I. J. H. Isbrücker. 1983. The mailed catfish genus Lasiancistrus Regan, 1904, from French Guiana and Surinam, with descriptions of two new species (Pisces, Siluriformes, Loricariidae). Bij. Dierk., 53: 33-48.

Isbrücker, I. J. H. 1980. Classification and catalogue of the mailed Loricariidae (Pisces, Siluriformes). Versl. Techn. Gegevens, Univ. van Amsterdam, 22: 1-181 pp.

Isbrücker, I. J. H., I. Seidel, J. P. Michels, E. Schraml and A. Werner. 2001. Diagnose vierzehn neuer Gattungen der Familie Loricariidae Rafinesque, 1815 (Teleostei, Ostariophysi). Datz: 17-24.

Leviton, A. E., R. H. Gibbs, E. Heal, & C. E. Dawson. 1985. Standards in herpetology and ichthyology: Part I. Standard symbolic codes for institutional resource collections in herpetology and ichthyology. Copeia, 1985: 802-832.

Sabaj, M.H., J.W. Armbruster, and L.M. Page. In Press. Spawning in Ancistrus with comments on the evolution of snout tentacles as a novel reproductive strategy: larval mimicry. Ichthyol. Explor. Freshwaters.

Taylor, W. R. & G. C. Van Dyke. 1985. Revised procedures for staining and clearing small fishes and other vertebrates for bone and cartilage study. Cybium 9: 107-119.

Weidner, T. 1996. Loricariiden aus Venezuela. DATZ 1996: 756.


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