GENETICS, EVOLUTION, AND PHYLOGENY - ORIGINAL PAPER Solving an old enigma: Morellospora saccamoebae gen. nov., sp. nov. (Rozellomycota), a Sphaerita-like parasite of free-living amoebae Daniele Corsaro 1 & Julia Walochnik 2 & Danielle Venditti 1 & Bärbel Hauröder 3 & Rolf Michel 3 Received: 12 December 2019 /Accepted: 5 February 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract The Rozellomycota form a lineage basal or sister to the Fungi, ancestor of Microsporidia. Their biodiversity is very rich but remains poorly characterized. The few known species are all parasites, whether of water molds and algae (Rozella), crustaceans (Mitosporidium), or as endonuclear parasites of amoebae (Nucleophaga, Paramicrosporidium). Since the nineteenth century, intracytoplasmic parasites of various protozoa have been described as species of the same genus Sphaerita. However, it was later thought possible to separate these parasites into at least two distinct groups, those forming flagellated zoospores, prevalent in Euglena and other flagellates, and those forming immobile spores, found mainly in free-living and endozoic amoebae. Herein, we report the recovery of a strain of the free-living amoeba species Saccamoeba lacustris, naturally infected by an intracytoplasmic parasite, which under light microscope has a morphology consistent with that of Sphaerita. Biomolecular analyses were thus performed. Our results show that the intracytoplasmic parasite of Saccamoeba belongs to the same subgroup of Mitosporidium and that it forms a new genus within Rozellomycota, Morellospora, that corresponds to the former spore-forming Sphaerita-like parasites of amoebae. Keywords Free-living amoebae . Microsporidia-like organisms . Morellospora . Rozellomycota . Sphaerita Introduction The prey-predator interactions between protists and fungi have been known since the nineteenth century, but they have remained largely unexplored. The ability of fungi to parasitize amoebae has been studied by various old authors, among which Drechsler with his research on predatory fungi (Drechsler 1941), and Dangeard, who reported various forms of parasites (Dangeard 1895, 1910) are particularly notewor- thy. Previous summaries of these studies were provided by Kirby (1941) and Ball (1969). The predaceous fungi of amoe- bae, also called amoebophagous fungi, belong mainly to the Zoopagales (Zoopagomycota) (Corsaro et al. 2018), which include only parasites of small invertebrates or other fungi, and to various anamorphic genera of Ascomycota and Basidiomycota (e.g., Drechsler 1964, 1969). Parasitic chytrids are mainly known and studied as phytoplankton parasites, but rare cases of chytrids preying on amoebae have been reported (Karling 1946). The old literature, however, reported various parasites of protozoa, living either in the nucleus or in the cytoplasm of the infected cell (Dangeard 1886, 1895). These were considered as chytrids and grouped with other intracel- lular parasites into one and the same family, the Olpidiaceae, within the Chytridiales (Sparrow 1960). Members of this fam- ily are mostly parasites of algae, other water molds (e.g., Rozella), plant roots (Olpidium), and freshwater crustaceans (Blastulidium). Their thallus is unicellular and lacks a rhizoi- dal system, and it is entirely converted into a sporangium to form posteriorly uniflagellate zoospores, with the exception of endoparasites of amoebae (Nucleophaga) which produce non- Handling Editor: Una Ryan * Daniele Corsaro corsaro@gmx.fr 1 CHLAREAS, 12 rue du Maconnais, F-54500 Vandoeuvre-lès-Nancy, France 2 Molecular Parasitology, Institute of Specific Prophylaxis and Tropical Medicine, Medical University of Vienna, Kinderspitalgasse 15, 1095 Vienna, Austria 3 Department of Pathology, Electron Microscopy Facility, Bundeswehr Central Hospital Koblenz, Andernacher Strasse 100, 56070 Koblenz, Germany Parasitology Research https://doi.org/10.1007/s00436-020-06623-5