Development and Molecular Characterisation of the Microsporidian Schroedera airthreyi n. sp. in a Freshwater Bryozoan Plumatella sp. (Bryozoa: Phylactolaemata)

. The development of a new species of microsporidian, infecting a freshwater Plumatellid bryozoan, is described. The small‐subunit rDNA, internal transcribed spacer region (ITS), and partial large‐subunit rDNA genes were sequenced. Phylogenetic analysis demonstrated that the parasite clustered with Schroedera plumatellae. However, while there were morphological affinities with this species, significant differences were also observed. The infection initially appeared as a roughening of the peritoneum lining the metacoelom of the bryozoan. This roughening resolved into meront‐infected syncytia, composed of interconnected cells of the body wall that detached to float in the coleomic cavity. Spores were observed to develop within these syncytia. All stages of development were diplokaryotic in contrast to S. plumatellae, which has a distinct monokaryotic merogony preceding sporogony. The infection was pathogenic to the host. Direct bryozoan–bryozoan transmission was not observed. We propose to name the microsporidian Schroedera aithreyi n. sp.