The Mussel of the Month is late this month because DLG was away to Lake Mweru in Zambia looking for live specimens of this very mollusk, so what better reason to recognize it for August 2009!
The taxonomy for this mussel is somewhat confused (or at least, we hypothesize that it is confused until we have more data to convince us otherwise). Everything about the outward appearance of M. mweruensis looks like it belongs in the large, garbage-pail genus Coelatura. Haas was the first one to single out this species as a subgenus, but it was Pain & Woodward (1968) that really tried to make a case for its uniqueness. They argued that,
"... since it differs from other African Unionids in details of its shell morphology and anatomical features, [it] is placed in a new subfamily Mweruellinae."
The anatomical feature to which Pain & Woodward referred was the fact that in the specimen(s) they examined, females brooded in only the inner demibranchs as opposed to all four like Coelatura. As far as the species unique conchology, they noted,
"... umbonal sculpture consisting of well developed radial plications highly reminescent of those of the South American genus Tetraplodon Spix (= Castalia of authors non Lamarck)... ."
 For the record, the specimens that we have seen (including the type pictured on this page) looking nothing like any species of Castalia. Some specimens do have weak umbonal sculpture, typical of Coelatura species of the region. Until now, we have not had any preserved specimens with soft-parts to confirm Pain & Woodward's other observations. However, DLG got a bunch in Lake Mweru this year, and we are looking forward to including them in future phylogenetic and anatomical studies.
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