Morphology of developmental stages of Rhytidocystis sp. n. (Agamococcidia) from White Sea polychaete Travisia forbesii
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| Year of publication | 2013 |
| Type | Conference abstract |
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| Description | Agamococcidia is a small group belonging to the phylum Apicomplexa inhabiting invertebrates from marine environment. Unlike other apicomplexans, such as Toxoplasma, Plasmodium and Cryptosporidium that are of great importance as human and animal pathogens, these parasites are not well studied. However, the knowledge about small groups like Agamococcidia, or Blastogregarina is crucial in our understanding of evolutionary pathways of the phylum Apicomplexa. Agamococcidia has unusual life cycle lacking gametogony and merogony. The genus Rhytidocystis has been originally established in 1907 by Henneguy for intestinal parasite of Ophelia bicornis. Recently, several new species of this genus were described from marine polychaetes Polygordius sp. and Travisia pupa. But no information on life cycle and morphology of different developmental stages of the genus Rhytidocystis spp. are available so far. Under the light microscopy, the parasites distribute uniformly along and around (at the cross sections) intestine of Travisia forbesii, and appear as white dots of uncertain shape. When taken out from the tissue they became oval in shape and demonstrate no cell motility. Histological and ultra-thin sections showed that several developmental stages of Rhytidocystis sp. may occur in intestinal epithelium of T. forbesii. One stage is oval-shaped. The cytoplasm is filled with lipid droplets, protein inclusions, amylopectine granules and round to oval nucleus with dense nucleolus. A lot of giant mitochondria with tubular cristae can be observed at the periphery closely adjacent to the pellicle. Other stage, oval to round in shape, possesses darker cytoplasm, filled with the same set of inclusions and more condense mitochondria. The last one stage is at least 2 times larger, the parasite pellicle forms a lot of invaginations. The cytoplasm is packed with numerous reserve granules, endoplasmic reticulum and central lobed nucleus. Some of these forms have rhizoid-like appendages. We assume that sporozoite of Rhytidocystis sp. penetrates through intestinal epithelium and start its development in connective tissue. During growth it modifies surrounding host cells. Later on a multinuclear syncytium from affected host cells develops around the parasite. We acknowledge the financial support from ECIP – Centre of excellence, GAČR No GBP505/12/G112 |
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