Petitella rhodostoma (Ahl, 1924) Bittencourt & Machado & Marshall & Hrbek & Farias, 2020

Bittencourt, Pedro Senna, Machado, Valéria Nogueira, Marshall, Bruce Gavin, Hrbek, Tomas & Farias, Izeni Pires, 2020, Phylogenetic relationships of the neon tetras Paracheirodon spp. (Characiformes: Characidae: Stethaprioninae), including comments on Petitella georgiae and Hemigrammus bleheri, Neotropical Ichthyology (e 190109) 18 (2), pp. 1-11 : 7

Petitella rhodostoma (Ahl, 1924) , new combination

Hemigrammus rhodostomus Ahl, 1924:405 , fig. unnumb. (original description; type-locality: Pará). — Ramsperger, 1924:810 (type-locality description: tributary of the Rio Tapajoz [Tapajós], Santarém, Pará).

Comparative remarks. Petitella georgiae is distinguished from its congeners by a long and wide maxillary (vs. very short and round in P. bleheri , and short in P. rhodostoma ); single row of premaxillary teeth (vs. two in P. bleheri and P. rhodostoma ); dentary with 9–11 teeth with 5 cuspids (vs. 6, with 6 or 7 cuspids, followed by 1 or 2 tricuspidate ones in P. bleheri , and 5–6 with 5 cuspids, usually followed by 4 conical teeth in P. rhodostoma ); absence of black spot on lower posterior border of caudal peduncle (vs. present in P. bleheri and P. rhodostoma ).

Petitella bleheri is distinguished from its congeners by the much more intense and widespread red color of the head, extending up to the humeral region (vs. limited red coloration and not extending to humeral region in P. georgiae and P. rhodostoma ); horizontal black bar on the end of the caudal peduncle is never prolonged forward (vs. prolonged up to the anal-fin in P. georgiae and P. rhodostoma ); anal-fin hyaline (vs. a black bar on the base of the anterior part of the anal-fin, continuing obliquely on the branched rays in P. georgiae and P. rhodostoma ).

Petitella rhodostoma is distinguished from its congeners by the red head color not extending to the humeral region and the presence of a black spot on the lower posterior border of the caudal peduncle (vs. head color not extending to humeral region with only one black spot on caudal peduncle in P. georgiae , and head color extending to humeral with two black spots on caudal peduncle in P. bleheri ); dentary with 5–6 teeth, with 5 cuspids, usually followed by 4 conical ones (vs. 9–11 teeth, with 5 cuspids in P. georgiae , and 6 teeth, with 6 or 7 cuspids, followed by 1 or 2 tricuspidate ones in P. bleheri ).