Clypeatula cooperensis gen. n., sp n., a new freshwater sponge (Porifera, Spongillidae) from the Rocky Mountains of Montana, USA

A new genus and species of freshwater sponge, Clypeatula cooperensis, colle cted from three lakes in the Northern Rocky Mountains of Montana, USA, are described. The sponge grows as a hard, disc-shaped encrustation on the unde rsides of rocks and logs. It lacks microscleres and has amphioxeal megascle res that often show a slight midregion bulb and are usually covered with sh ort, conical spines except at their tips. The sponge is also non-gemmulatin g, overwintering in a regressed state in which choanocyte chambers are redu ced in number. Phylogenetic analyses of complete 18S rDNA sequences of C. c ooperensis, Ephydatia muelleri, Spongilla lacustris and Eunapius fragilis s uggest that C. cooperensis is more closely related to Ephydatia muelleri th an to Spongilla lacustris or Eunapius fragilis. Our data, nonetheless, do n ot rule out the possibility that C. cooperensis is more closely related to the non-gemmulating sponges of Lake Baikal (Russia) than it is to Ephydatia muelleri. These phylogenetic analyses support the erection of a new genus, the monophyly of freshwater sponges belonging to the families Spongillidae and Lubomirskiidae, and the monophyly of demosponges.