Protocheirodon, Vari & Melo & Oliveira, 2016

Vari, Richard P., Melo, Bruno F. & Oliveira, Claudio, 2016, Protocheirodon, a new genus of Characidae (Teleostei: Characiformes) with the redescription of the poorly known Protocheirodon pi, Neotropical Ichthyology 14 (2), No. e 150154, pp. 1-7 : 2-3

Protocheirodon , new genus

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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 typespecies, 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.

Figures

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.