Mussel of the Month

UMMZ 110009. India (ex Rolle 27 November 1909)

A few years ago, we didn't recognize Radiatula as a valid genus. Rather, we followed previous authorities by treating Radiatula as a subgenus of Parreysia (e.g., Subba Rao, 1989). Furthermore, we used to be fuzzy about the phylogenetic position of Parreysia relative to the other unionid genera. We "punted" and just put most of the tropical taxa in a big group called "incertae sedis Old World unionids" (Graf & Cummings, 2007). Click here to go back in time and see the old classification applied on this web site.

The situation changed once we had some phylogenetic data. Whelan et al. (2011) demonstrated not only that Radiatula was distinct from Parreysia, but the two taxa are found in distinct lineages of a large clade of Indian and African taxa. Based on their phylogeny, we recognize four tribes in the subfamily Parreysiinae: Parreysiini, Lamellidentini, Oxynaiini, and Coelaturini. Parreysia (obviously) was recovered in the Parreysiini, but Radiatula came out in the Oxynaiini.

This is an exciting result, but there is still more work to be done. Most significantly, Whelan et al. (2011) only examined a single species of Radiatula, R. bonneaudii. It remains to be seen whether the traditional circumscription of Radiatula is monophyletic. In the absence of a definitive test, we are stuck extrapolating from the meager data that are available.

Classification:

Phylum Mollusca
Class Bivalvia
Subclass Palaeoheterodonta
Order Unionoida

Family UNIONIDAE Rafinesque, 1820
Subfamily PARREYSIINAE Henderson, 1935
Tribe OXYNAIINI Starobogatov, 1975

Genus Radiatula Simpson, 1900

Species Radiatula crispisulcata (Benson, 1862)