Sunday, June 26, 2016

[Ichthyology • 2016] Protocheirodon gen. nov. • A New Genus of Characidae (Characiformes) with the Redescription of the Poorly Known Protocheirodon pi

Protocheirodon pi 
 (Vari, 1978) DOI: 10.1590/1982-0224-20150154


Protocheirodon, a new genus of the Characidae, is proposed to include a species previously assigned to Leptagoniates . This action is supported by molecular and morphological phylogenetic hypotheses that place Protocheirodon pi as the sister group of the remaining tribes in the Cheirodontinae versus the traditional assignment of the species to the Aphyocharacinae. The phylogenetic position of Protocheirodon is recognized as a new tribe, the Protocheirodontini. Protocheirodon pi , originally described based on a small number of specimens from a single location in the río Mamoré basin in the southwestern Amazon, is redescribed on the basis of larger series of specimens from the western and central portions of the Amazon basin.

Key words: Aphyocharacinae; Amazon basin; Cheirodontinae; Leptagoniates; Taxonomy

Fig. 2 Protocheirodon pi, (A) CAS 41749, 29.5 mm SL; Colombia, Amazonas, Isla de Santa Sofia II, ca. 20 mi (= 32 km) NW of Leticia; (B) live specimen from aquarium without locality information.
Scale bar = 5 mm. Photo credits: (A) Sandra Raredon (USNM) and (B) Martin and Peter Hoffmann. DOI: 10.1590/1982-0224-20150154


Protocheirodon, new genus

Type species. Protocheirodon pi (Vari, 1978).

Diagnosis. Protocheirodon possesses the four synapomorphies proposed for the Cheirodontinae by Malabarba (1998): 1) the presence of a pseudotympanum, a hiatus in the body wall musculature lateral to at least a portion of the anterior chamber of the swimbladder; 2) the lack of a dark humeral spot; 3) the possession of pedunculate dentition; and 4) the presence of only a single row of regularly arranged premaxillary teeth. Protocheirodon differs from all other genera of the Cheirodontinae and indeed members of the Characiformes by the unique form of the swimbladder which has a smaller rotund anterior chamber and the posteriorly chamber elaborated into two vertically elongate, side by side, slightly inclined chambers. These modifications yield a unique overall pi (π)-shaped structure (Vari, 1978) (Fig. 2). This trenchant difference versus other cheirodontins is supplemented by a diagnostic combination of meristic, morphometric and details of pigmentation.

Description. As Protocheirodon is a monotypic genus, its description corresponds to the redescription of the type-species, Protocheirodon pi (Vari, 1978).

Etymology. Proto from Greek prōto , meaning first or earliest form of, in reference to the phylogenetic position of the species as sister to all remaining members of the Cheirodontinae, and cheirodon, an allusion to the genus Cheirodon and subfamily Cheirodontinae. Gender masculine.

Protocheirodon pi (Vari, 1978)
Leptagoniates pi Vari, 1978: 185, figs. 1-2 (original description; río Mamoré, Bolivia). -Malabarba, 1998: 229 (in phylogeny of Cheirodontinae). Lima et al., 2003: 144 (in list of incertae sedis species in Characidae). -Bogotá-Gregory & Maldonado-Ocampo, 2006: 66 (in list of fishes in Colombian Amazon). -Maldonado-Ocampo et al. , 2008: 170 (Colombia, Amazon; in checklist of freshwater fishes of Colombia). -Duarte et al., 2010: 323 (in list of fishes from lower rio Purus, Brazil). Ortega et al., 2010: 36 (in list of freshwater fishes of Peru). -Lima et al. , 2013: 299 (in list of fishes from rio Madeira, Brazil). -Tagliacollo et al., 2012: 305 (in molecular phylogeny of Aphyocharacinae). -Mariguela et al., 2013: 29 (in molecular phylogeny of Cheirodontinae).

Diagnosis. As for Protocheirodon above.

Description. Summary morphometrics in Table 1. Body distinctly compressed and moderately elongate with greatest depth immediately anterior to dorsal-fin origin. Dorsal profile of head convex from margin of upper lip to vertical through anterior margin of orbit and then very slightly concave to rear of head. Predorsal profile of body straight to very slightly sigmoid. Dorsal profile strongly posteroventrally angled along dorsal-fin base and then straight and less posteroventrally angled to caudal peduncle. Ventral profile of head and body gently convex from tip of lower jaw to anal-fin origin, straight and posterodorsally angled along anal-fin base to caudal peduncle.

Richard P. Vari, Bruno F. Melo and Claudio Oliveira. 2016. Protocheirodon, A New Genus of Characidae (Teleostei: Characiformes) with the Redescription of the Poorly Known Protocheirodon pi.  Neotrop. ichthyol. 14(2); DOI: 10.1590/1982-0224-20150154 

RESUMO: Protocheirodon, um gênero novo de Characidae é proposto para incluir uma espécie previamente alocada em Leptagoniates . Esta decisão é suportada por hipóteses filogenéticas moleculares e morfológicas que apontam Protocheirodon pi como grupo-irmão das demais tribos de Cheirodontinae, ao invés da alocação tradicional em Aphyocharacinae. A posição filogenética de Protocheirodon é reconhecida como uma tribo nova, Protocheirodontini. Protocheirodon pi , originalmente descrito com base em poucos exemplares de uma única localidade na bacia do rio Mamoré, no sudoeste da Amazônia, é redescrito com base em grandes séries de espécimes coletados em rios das porções centrais e ocidentais da bacia do rio Amazonas.