Thursday, February 16, 2017

[Ichthyology • 2017] Phycocharax rasbora • A New Genus and Species of Brazilian Tetra (Characiformes: Characidae) from Serra do Cachimbo, rio Tapajós Basin

Phycocharax rasbora
Ohara, Mirande & de Lima, 2017 

A new genus and species of characid fish is described from rio Braço Norte, a tributary of rio Teles Pires, Tapajós basin, Mato Groso, Brazil. The new taxa can be diagnosed from the remaining characids by a unique combination of characters that includes the presence of a single row of relatively compressed premaxillary teeth, large teeth with four to nine cusps on premaxillary and dentary, absence of pseudotympanum, incomplete lateral line with 7–13 pored scales, sexually-dimorphic males with distal margin of anal fin approximately straight, and presence of a nearly triangular and horizontally elongated blotch from the posterior half of the body to caudal peduncle. The most parsimonious phylogenetic hypothesis, using morphological data, recovered the new genus and species in a clade including Paracheirodon axelrodi and Hyphessobrycon elachys.

Fig 3. Phycocharax rasbora, MZUSP 119843, paratype, 29.1 male (a) and MZUSP 115313, paratype, 26.4 mm SL, female (b), immediately after collection. 

Family Characidae Agassiz

Phycocharax, new genus.

Type species: Phycocharax rasbora, new species, by monotypy and original description.

Diagnosis: Phycocharax can be diagnosed from the remaining characid genera by the combination of the following character-states, none of them unique: 1) presence of single row of relatively compressed premaxillary teeth (Fig 2); 2) large teeth on premaxillary, and dentary with four to nine cusps (Fig 2); 3) pseudotympanum absent; 4) incomplete lateral line with 7–13 pored scales; 5) anal fin dimorphic, males with distal margin approximately straight, and decreasing gently posteriorly (Figs 1a and 3a), while females present slightly concave margin of anal fin with anteriormost branched rays distinctly longer than remaining rays (Figs 1b and 3b); 6) presence of horizontally-elongated somewhat triangular blotch extending from vertical through dorsal-fin terminus to caudal peduncle end (Figs 1 and 3).

Etymology: From the Greek phykos, meaning “algae”, in allusion to the feeding habit of the new taxon owing to the dominance of this resource in its stomach contents, plus charax, meaning “pointed stake” or “palisade of pointed sticks”, the first generic name in Characidae. Gender masculine.

Phycocharax rasbora, new species.

Distribution: Phycocharax rasbora is so far known only from its type locality at upper rio Braço Norte, a right-bank tributary of the rio Peixoto de Azevedo, part of rio Teles Pires drainage, rio Tapajós basin (Fig 5). The rio Braço Norte drains the Serra do Cachimbo at northern Mato Grosso State, Brazilian Amazon.

Etymology: From the Bengali word “rasbora”, the common name of the fish Rasbora rasbora (Hamilton). Rasbora is a generic name encompassed a great radiation of small cyprinids from southeastern Asia, including the species currently allocated in the genus Trigonostigma, which possess a dark triangular blotch on body sides very reminiscent in shape and position similarly as found in the new species. Gender masculine. A noun in apposition.

Willian Massaharu Ohara, Juan Marcos Mirande and Flávio Cesar Thadeo de Lima. 2017. Phycocharax rasbora, A New Genus and Species of Brazilian Tetra (Characiformes: Characidae) from Serra do Cachimbo, rio Tapajós Basin.
  PLoS Biology. DOI: 10.1371/journal.pone.0170648