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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 7739

Wilhelm Foissner and Ilse Foissner; First Record of an Ectoparasitic Flagellate on Ciliates: An Ultrastructural Investigation of the Morphology and the Mode of Attachment of Spiromonas gonderi Nov. Spec. (Zoomastigophora, Spiromonadidae) Invading the Pellicle of Ciliates of the Genus Colpoda (Ciliophora, Colpodidae). Protistologica XX(4):635-648, 1984

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A flagellate ectoparasitic on ciliates occurred spontaneously in a soil sample. It was first described by Gonder (1910) as "Colpoda-Parasit", but its flagellate nature was not recognized. Thus -as far as we know- this is the first reliable record of an extoparasitic flagellate on ciliates. Its fine structure and mode of life show that it is related to the genus Spiromonas. We think it is a new species, Spiromonas gonderi nov. spec., because it is host-specific for ciliates of the genus Colpoda and does not have a rostrum. Heavily infested hosts move more slowly than normal; their cytoplasm becomes strongly vacuolated and then they die. Light- and electron-microscopic examination reveals the following peculiarities, some of which are different from those described by Brugerolle and Mignot (1979) for S. perforans: 1. The left flagellum arises from a periflagellar canal, the right one directly from the cell surface. By contrast both flagella of S. perforans emerge from shallow depressions. 2. The pellicle consists of 3 unit membranes and is perforated by many micropores. There are subpellicular microtubules and a netlike fibro-granular layer on the surface of the pellicle. This surface coat is not demonstrable in S. perforans. 3. The anterior region of the parasite contains many micronemes. 4. The host-parasite connection is mediated by a complex "apical apparatus" that consists of a ring of 4-5 microtubules, a polar ring-like structure, and a unit membrane that separates the host from the parasite. The separating membrane is made of the inner electron-dense layers of the cell membrane of the ciliate and parasite respectively. We suppose that nutritive substances must pass through this membrane, because S. gonderi lacks a true cytostome and feeding is a long-lasting process in this species. Lytic enzymes released from the micronemes could be of importance during this procedure. No comparable "apical apparatus" has been described for S. perforans. 5. The cristae mitochondriales are tubular. 6. Unlike S. perforans, which has a contractile vacuole and trichocysts of the dinoflagellate type, S. gonderi did not exhibit such organelles. These fine structural peculiarities, especially the "apical apparatus", suggest a close affinity of Spiromonas to the Sporozoa. Thus one may speculate that this enigmatic creature might be either a developmental stage of a coccidian or a coccidian that has turned secondarily to an ectoparasitic mode of life. But if we consider the flagellated trophic stage of Spiromonas, it is more likely that the Spiromonadidae are nearer to the Zoomastigophora than to the Sporozoa.