Lanatospora costatasp. n., a new microsporidian parasite of the adipose and connective tissue cells of Megacyclops viridis (Jurine, 1820) (Copepoda: Cyclopidae) is described. It was isolated from a woodland pool with a rich and diverse fauna of microsporidia-infected small crustaceans and insect larvae. The parasite is structurally similar to the genus Lanatospora Voronin, 1989, characterized by a complex decorated exospore. In the described species the exospore is armoured by a conspicuous layer of interwoven ribs forming labyrinth on the spore surface. SSU rRNA phylogeny places the organism in the “aquatic outgroup” of microsporidia (Vossbrinck et al. 2004), which includes a number of microsporidia from aquatic microcrustacea of the classes Copepoda and Cladocera. The increasing number of available SSU rRNA gene sequences of these microsporidia allows a more detailed interpretation of their developmental histories.
