A three-species problem: a further example of homeomorphy in freshwater Ostracoda (Crustacea), with the description of a new genus and new species from a Brazilian river

Homeomorphy is common in the valves and carapaces of Ostracoda. One of the best-known examples in non-marine ostracods is the morphological similarity in the extreme armature of anterior and posterior spines on the left valve in both Strandesia bicornuta Hartmann, 1964 from India and in Rudjakoviella prolongata (Triebel, 1962) Malz, 1973 from Margarita Island (West Indies). Here, we describe a third representative with such armature, Pseudocypricercus bonito gen. nov. spec. nov. from Brazil. These new taxa belong to the Cypricercinae McKenzie, 1971, which is characterized by the presence of the Triebel's loop in the middle of the attachment of the caudal ramus. The main characteristics of Pseudocypricercus gen. nov. are the shape and length of the β seta on the mandibular palp, which is slender and elongated, compared to other genera of this subfamily; the absence of seta d on the first thoracopod, and the absence of seta d2 on the second thoracopod, amongst other features. Pseudocypricercus bonito gen. nov. spec. nov. also has large anterior and posterior spines on the left valve as well as a posterior spine and the anterior blunt protrusion on the right valve. In addition, both the mandibular coxa and the third endite of the maxillula have remarkable large fist-like setae, while the male right prehensive palp has a perpendicularly positioned second segment. The similar armature on left valve and right valve in this taxon makes the homeomorphy known from R. prolongata and S. bicornuta into a “three-species problem”.