Pleuroxus Baird 1843

Genus Pleuroxus Baird, 1843

According to Smirnov (1996), Pleuroxus is one of the most difficult genera of Chydorinae. Barcoding distinguished two species, both in the north: P. varidentatus Frey and P. denticulatus Birge. The latter species was recently recorded from southern Mexico (Elías-Gutiérrez et al. 2006). Smirnov (1996) suggested that the subgenus Picripleuroxus should be raised to a genus level, but Chiambeng & Dumont (2004) did not support this shift. The high barcode divergences (>20%) between the two species of Pleuroxus supports Smirnov’s stance and accords with Sacherova & Hebert’s (2003) proposal that Pleuroxus should be divided into several genera. Recently, Smirnov et al. (2006) concluded that the phylogeny of Pleuroxus is still not resolved sufficiently to be able to decide on generic or subgeneric boundaries, making it clear that further investigation is required.

In general our data for the family Chydoridae agree well with conclusions on generic and species boundaries proposed by Sacherova & Hebert (2003). For example Alona is not monophyletic, and should be partitioned into more than two genera. Part of this work has been done, e.g. the proposal of the new genus Leberis by Smirnov (1989), but work remains as shown in the case of Alona dentifera. The deep divergences found in all groups confirm the hypothesis of an ancient origin for all chydorid lineages.