A reappraisal of the type series of the early Cretaceous margaritiferid ‘Unio’ valdensis Mantell, 1844

Abstract

This study re-examines the type series of the Early Cretaceous freshwater bivalve Unio valdensisMantell, 1844, in relation to the assignment of the species to the genus ParaheudeanaStarobogatov (1970), and the subgenus Pseudunio by Mongin (1961). For the first time, we recognise the type specimens as incomplete lacking critical posterior portions of the shell. We observe that the lectotype, superficially oval in outline, has a shallow, but distinct postero-ventral sinus, seemingly out-grown, the broken ventral margin not preserving actual shell shape or the commissure. Significantly, many other specimens confirm the presence of the postero-ventral sinus and elongate-oval outline. It is unclear why Starobogatov removed Margaritifera (Pseudunio) valdensis but maybe the perceived oval outline was sufficient for separation. Combined with diagnostic characters such as mantle pits, we retain the freshwater mussel Unio valdensis in the genus Margaritifera and refute the validity of the genus ParaheudeanaStarobogatov (1970). Araujo et al. (2016) reviewing the phylogeny of the Margaritiferidae, concluded only the genus Margaritifera was valid, discounting Pseudunio as a valid genus or subgenus, placing further doubt upon the use of the then subgenus, conversely more recent studies have supported the genus Pseudunio promoting it to a genus.