Taxonomy on three novel species of Sphaeromyxa Thelohan 1892 (Myxozoa, Bivalvulida, Sphaeromyxidae) with insight into the evolution of the genus.

Three new myxosporeans of the genus Sphaeromyxa Thelohan 1892 were discovered from the coastal waters off Xiamen in the East China Sea and characterized based on morphological and SSU rDNA data. Sphaeromyxa photopectoralis sp. n. was described from Photopectoralis bindus, and Sphaeromyxa sebastisca sp. n. was described infecting both Sebastiscus marmoratus (type-host) and Scorpaenopsis cirrosa. These two species are morphologically consistent with the "balbianii" group, possessing straight myxospores and truncated ends, but are distinct from one another genetically and by myxospore dimensions. A third myxosporean infecting Siganus fuscescens was described as Sphaeromyxa xiamenensis sp. n., and this species is morphologically consistent with the "incurvata" group, bearing arcuate myxospores with rounded ends. The molecular phylogeny and estimated rRNA secondary structure suggest that marine sphaeromyxids are probably derived from freshwater myxidiids, and "incurvata" and "balbianii" groups might each represent independent evolutionary lineages. The present study also shows that S. limocapitis phylogenetically nested in "incurvata" group.