Diplonemids are a hyperdiverse group of flagellated protists, but with less than two dozen formally described representatives. Here, we describe four new species of cultured diplonemids, identified on the basis of their 18S rRNA sequences, light-, fluorescence-, scanning- and transmission electron microscopy. Three new species belong to the genus Rhynchopus (R. asiaticus sp.n., R. granulatus sp.n., and R. valaseki sp.n.), while the fourth species is an unusual representative of the genus Lacrimia (L. aflagellata sp.n.). The latter organism is the first diplonemid outside the genus Rhynchopus (as defined previously) to show a gliding trophic stage with flagellar stubs concealed inside the flagellar pocket and a highly motile dispersive swimming stage. Since this character is thus no longer a genus-specific apomorphy, we provide a taxonomic revision of the genus Rhynchopus with separation of the new genus Natarhynchopus gen. n. We also identify bacterial endosymbionts of L. aflagellata and R. asiaticus as Ca. Syngnamydia medusae (Chlamydiales, Simkaniaceae) and Ca. Cytomitobacter rhynchopi sp. n. (Alphaproteobacteria, Holosporaceae), respectively, and discuss their potential functions. This is the first report of a chlamydial symbiont within a diplonemid host. We also propose that diplonemids may serve as vectors for chlamydial pathogens of marine fish.

Institute of Evolutionary Biology Faculty of Biology University of Warsaw Warsaw Poland

Institute of Parasitology Biology Centre Czech Academy of Sciences České Budějovice Czech Republic; Faculty of Science University of South Bohemia České Budějovice Czech Republic

Institute of Parasitology Biology Centre Czech Academy of Sciences České Budějovice Czech Republic; Faculty of Sciences Charles University Prague Czech Republic

Japanese Agency for Marine Earth Science and Technology Yokosuka Japan; Advanced Institute for Marine Ecosystem Change Yokohama Kanagawa 236 0001 Japan

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