Blastogregarines are poorly studied parasites of polychaetes superficially resembling gregarines, but lacking syzygy and gametocyst stages in the life cycle. Furthermore, their permanent multinuclearity and gametogenesis by means of budding considerably distinguish them from other parasitic Apicomplexa such as coccidians and hematozoans. The affiliation of blastogregarines has been uncertain: different authors considered them highly modified gregarines, an intermediate apicomplexan lineage between gregarines and coccidians, or an isolated group of eukaryotes altogether. Here, we report the ultrastructure of two blastogregarine species, Siedleckia nematoides and Chattonaria mesnili, and provide the first molecular data on their phylogeny based on SSU, 5.8S, and LSU rDNA sequences. Morphological analysis reveals that blastogregarines possess both gregarine and coccidian features. Several traits shared with archigregarines likely represent the ancestral states of the corresponding cell structures for parasitic apicomplexans: a distinctive tegument structure and myzocytotic feeding with a well-developed apical complex. Unlike gregarines but similar to coccidians however, the nuclei of male blastogregarine gametes are associated with two kinetosomes. Molecular phylogenetic analyses reveal that blastogregarines are an independent, early diverging lineage of apicomplexans. Overall, the morphological and molecular evidence congruently suggests that blastogregarines represent a separate class of Apicomplexa.

Belozersky Institute of Physico Chemical Biology Lomonosov Moscow State University Leninskiye Gory 1 40 119 234 Moscow Russian Federation; Institute for Information Transmission Problems Russian Academy of Sciences Bolshoy Karetny per 19 1 127 051 Moscow Russian Federation

CNRS 7245 Molécules de Communication et Adaptation Moléculaire UMR 7245 CP 52 rue Cuvier 75005 Paris France

Department of Botany and Zoology Faculty of Science Masaryk University Kotlářská 2 611 37 Brno Czech Republic

Department of Invertebrate Zoology Faculty of Biology Saint Petersburg State University Universitetskaya emb 7 9 199 034 St Petersburg Russian Federation

Faculty of Biology Lomonosov Moscow State University Leninskiye Gory 1 12 119 234 Moscow Russian Federation

Sorbonne Université Université Pierre et Marie Curie Paris 6 CNRS UMR 7144 Station Biologique de Roscoff Place Georges Teissier CS90074 29688 Roscoff Cedex France

References provided by Crossref.org

Reconstruction of Plastid Proteomes of Apicomplexans and Close Relatives Reveals the Major Evolutionary Outcomes of Cryptic Plastids

Evidence from the resurrected family Polyrhabdinidae Kamm, 1922 (Apicomplexa: Gregarinomorpha) supports the epimerite, an attachment organelle, as a major eugregarine innovation

Nutrient Acquisition and Attachment Strategies in Basal Lineages: A Tough Nut to Crack in the Evolutionary Puzzle of Apicomplexa

Motility and cytoskeletal organisation in the archigregarine Selenidium pygospionis (Apicomplexa): observations on native and experimentally affected parasites