Agamococcidiorida Levine 1979

Introduction

This group of Apicomplexa is characterised by the absence of merogony and gametogony. In taxonomical texts it is referred to as Order Agamococcidiorida Levine, 1979. There are two families recognised:

Family: Rhytidocystidae Levine, 1979

Genus: Rhytidocystis Henneguy, 1907 (=Dehornia Porchet-Hennere, 1972)
Only ~4 species recognised from marine annelids and polychaetes. Type species: Rhytidocystis opheliae Henneguy, 1907 (from Ophelia bicornis)

Family: Gemmocystidae Upton & Peters, 1986

Genus: Gemmocystis Upton & Peters, 1986
A single species found in Caribbean scleractinian corals (Cnidaria). Type species: Gemmocystis cylindrus Upton & Peters, 1986 (from Dendrogyra cylindrus)

Discussion of Phylogenetic Relationships

Only Rytidocystis polygordiae has been characterised using electron microscopy and phylogenetic analyses of small subunit (SSU) rDNA sequences (Leander & Ramey 2006). It is the first available sequence for this group of apicomplexans. The intracellular sporozoites posses a conoid, rhoptries, micronemes, dense granules, and a posteriorly positioned nucleus. The phylogeny indicates a close relationship between R. polygordiae with some environmental phylotypes of unknown morphological identity. The sequence branches at the unresolved base of Apicomplexa and contradicts the traditional placement within the coccidian group. The basal radiation of apicomplexa sufferes from (i) poor taxon sampling and (ii) inability of SSU rDNA to resolve this region.

Very little is known about the coral parasite Gemmocystis (Upton and Peters, 1986). The molecular identity of these presumably coccidian parasites remains puzzling. While there is not yet a true sequence of Gemmocystis, there are a few sequences that are apparently from a coral apicomplexan (Toller et al., 2001 & 2002). Whether these coral reports apply to Gemmocystis is not clear but deserve further scrutiny.

References

Leander, B. S., and P. A. Ramey. 2006. Cellular identity of a novel small subunit rDNA sequence clade of apicomplexans: Description of the marine parasite Rhytidocystis polygordiae n. Sp (Host : Polygordius sp., polychaeta). Journal of Eukaryotic Microbiology 53:280-291.

Levine, N. D. 1979. Agamococcidiorida ord. n. and Rhytidocystidae fam. n. for the Coccidian genus Rhytidocystis Henneguy, 1907. Journal of Protozoology 26:167-168.

Toller, W. W., R. Rowan, and N. Knowlton. 2001. Zooxanthellae of the Montastraea annularis species complex: Patterns of distribution of four taxa of Symbiodinium on different reefs and across depths. Biological Bulletin 201:348-359.

Toller, W. W., R. Rowan, and N. Knowlton. 2002. Genetic evidence for a protozoan (phylum Apicomplexa) associated with corals of the Montastraea annularis species complex. Coral Reefs 21:143-146.

Upton, S. J., and E. C. Peters. 1986. A new and unusual species of coccidium (Apicomplexa: Agamococcidiorida) from Jamaican scleractinian corals. J. Invert. Pathol. 47:184-193.