Edinburgh Napier University

  A new Rhytidocystis species is described from the north-eastern Pacific Coast. Trophozoites of R. cyamus sp. n. were isolated from the intestines of the opheliid polychaete Travisia pupa, collected from mud dredged at a depth of 80 m. The trophozoites of R. cyamus sp. n. were relatively small (40–64 μm long, 27–30 μm wide) and bean-shaped with a centrally located nucleus. The trophozoite surface was inscribed by 10–12 longitudinal rows of short transverse folds and less conspicuous grooves with an irregular pattern. Micropores were observed in association with the transverse folds. A mucron or apical complex was not observed with either light or scanning electron microscopy. The trophozoites did not show any degree of motility. The SSU rDNA sequence obtained from R. cyamus sp. n. clustered strongly with R. polygordiae within the rhytidocystid clade. Although the precise phylogenetic position of the rhytidocystid clade within the Apicomplexa remains uncertain, the rhytidocystid sequences diverged with a weak affinity to a terrestrial clade containing cryptosporidians, neogregarines and monocystids.