''Pseudolithoxus'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of suckermouth armored catfishes with five described species from the basins of the

Orinoco The Orinoco () is one of the longest rivers in South America at . Its drainage basin, sometimes known as the Orinoquia, covers approximately 1 million km2, with 65% of it in Venezuela and 35% in Colombia. It is the List of rivers by discharge, f ...

Casiquiare The Casiquiare river or canal () is a natural distributary of the upper Orinoco flowing southward into the Rio Negro, in Venezuela, South America. As such, it forms a unique natural canal between the Orinoco and Amazon river systems. It is the ...

and upper Rio Negro in

Venezuela Venezuela, officially the Bolivarian Republic of Venezuela, is a country on the northern coast of South America, consisting of a continental landmass and many Federal Dependencies of Venezuela, islands and islets in the Caribbean Sea. It com ...

. Additionally, a possibly

undescribed species In taxonomy, an undescribed taxon is a taxon (for example, a species) that has been discovered, but not yet formally described and named. The various Nomenclature Codes specify the requirements for a new taxon to be validly described and named. U ...

is known from the

Trombetas The Trombetas is a large river on the northern side of the Amazon River. Course The Trombetas is long, and is navigable by 500 ton vessels for a stretch of . The Trombetas river gives birth to very many rivers, including the Anamu river. It is ...

and

Nhamundá Nhamundá is the easternmost municipality in the Brazilian state of Amazonas. Its population was 21,443 (2020) and its area is 14,106 km².IBGE The Brazilian Institute of Geography and Statistics (; IBGE) is the agency responsible for o ...

rivers in Brazil.

Taxonomy

The species group was originally described in 2000 and the four species were temporarily placed in ''

Lasiancistrus ''Lasiancistrus'' is a genus of suckermouth armored catfishes. They are native to South America and Panama. Taxonomy ''Lasiancistrus'' was first described as a subgenus of ''Ancistrus'' in 1904, including ''A. heteracanthus'', ''A. pictus'', '' ...

''. In 2001, the genus ''Pseudolithoxus'' was erected for these species. This group forms a

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

to ''Lasiancistrus'' and ''

Ancistrus ''Ancistrus'' is a genus of nocturnal freshwater fish in the family Loricariidae of order Siluriformes, native to freshwater habitats in South America and Panama. Fish of this genus are common in the aquarium trade where they are known as bushy ...

''. ''P. anthrax'' and ''P. nicoi'' likely represent sister species. In 2011, ''P. kelsorum'' was described based on type material from Venezuela.

Species

There are currently six recognized species in this genus: * '' Pseudolithoxus anthrax'' ( Armbruster & Provenzano, 2000) * '' Pseudolithoxus dumus'' ( Armbruster & Provenzano, 2000) * '' Pseudolithoxus kelsorum'' ( Lujan & Birindelli, 2011) * '' Pseudolithoxus kinja'' Bifi, de Oliveira, Rapp Py-Daniel & Collins, 2018 * '' Pseudolithoxus nicoi'' ( Armbruster & Provenzano, 2000) * '' Pseudolithoxus tigris'' ( Armbruster & Provenzano, 2000)

Description

The largest ''Pseudolithoxus'' species reach up to in

standard length Fish measurement is the measuring of individual fish and various parts of fish anatomy, their anatomies, for data used in many areas of ichthyology, including Taxonomy (biology), taxonomy and fishery biology. Overall length Standard length (SL) is ...

. The genus is characterized by evertible cheek plates, a very dorsoventrally flattened body, extremely hypertrophied

odontode Odontodes, or dermal teeth, are hard structures found on the external surfaces of animals or near internal openings. They consist of a soft pulp surrounded by dentine and covered by a mineralized substance such as enamel, a structure similar to t ...

s (integumentary teeth) on elongated pectoral spines and along the snout margin, and 3 rows of plates on the

caudal peduncle Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...

. In addition, it appears as if females as well as males develop hypertrophied snout and pectoral-fin odontodes, traits normally restricted to nuptial males in other loricariids. ''Pseudolithoxus'' species may be differentiated based on colouration. Two species are black, usually with white spots, and lack dark bands on the

caudal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...

; ''P. nicoi'' has a white band at the

distal Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position provi ...

margin of the caudal fin, while ''P. anthrax'' does not. ''P. dumus'' has a colour pattern consisting of black spots on the head and anterior part of body, while ''P. tigris'' has a colour pattern consisting of brown and tan bars on the head and anterior part of body. However, ''P. dumus'' and ''P. tigris'' may actually both represent more species. In ''P. dumus'', specimens from northern Amazonas have a well-spotted caudal peduncle, those from the Ventuari and Cataniapo Rivers have spots along the mid-line on the caudal peduncle, and those from the Casiquiare have spots combining to form bands on the caudal peduncle. In some ''P. tigris'', though specimens have similar colour patterns, they may differ in thickness of the tan bars and dark bars, body depth, and eye position. The body of these fish is very dorsoventrally flattened with both ventral- and dorsal-surface flat. The dorsal fin spine is weak, and the dorsal fin spinelet supports odontodes. The pectoral fins are usually elongated, reaching the anus in juveniles and growing to the anal fins in the adults; ''P. anthrax'' has been referred to as "flying catfish", probably due to these long pectoral fins in adults. The caudal fin is weakly forked, with the lower lobe longer than the upper. The eyes are mostly dorsal. The abdomen is without plates.

References

{{Taxonbar, from=Q929277 Ancistrini Fish of Venezuela Endemic fauna of Venezuela Catfish genera Taxa named by Isaäc J. H. Isbrücker Taxa named by André Werner Freshwater fish genera