ИСТИНА

Digyalum oweni is a gut parasite of gastropods Littorina littorea, L. obtusata, and L. saxatilis. The trophozoites are capable of considerable changing their pear-shaped body (metaboly). Their surface is covered with folds, which are arranged perpendicularly to the longitudinal cell axis and form a kind of spiral. D. oweni has apical complex organelles (except for conoid) in the mucron part of the cell (Dyson et al., 1993; 1994; Dyson et al., 1995). Apicomplexans Platyproteum (formerly Selenidium) vivax and Filipodium spp. also move by metaboly; their cortex structure resembles that of archigregarines (however P.vivax forms surface folds of the same kind as D. oweni). Their apical complex seems to be reduced completely; and they are probably capable of phagocytosis on the anterior part of the cell (Hoshide & Todd, 1992, 1996; Leander, 2006; Rueckert & Leander, 2009). We have sequenced D. oweni SSU rRNA gene. Together with several unidentified environmental sequences, it forms a basal branch to P.vivax+Filipodium phascolosomae. Formerly the clade P. vivax+F. phascolosomae has occupied an uncertain place within Alveolata because of extreme length of the branch. Addition of D. oweni as a relatively short branch to these sequences enabled us to place the clade as a whole inside Apicomplexa, but without grouping it with some archigregarines, despite their common features, or with other sporozoans. We propose that this group forms a separate branch of Sporozoa. However, the life cycles of these protists are unknown; therefore their affinity to gregarines (presence of syzygy+gametocyst) or coccidia (lack of progamic mitosis in macrogamonts) is subject to further investigation.