| Popis |
Antarctic is an exceptional continent of the Earth with very extreme environment. Not many species can survive there, however, the marine fauna is enormously rich, especially in plankton, nekton and benthos. Many reviews concern climatology, geology, palaeontology, and fauna of vertebrates (fish, birds and mammals) of Antarctic (Eastman 2005; Barbosa and Palacios 2009). A number of investigations were dedicated to apicomplexans parasitizing fish, birds, and plankton krill (Barber and Mills Westermann 1988; Takahashi et al. 2009; Golemansky 2011). Only few studies, however, dealt with gregarines – one of the basal groups of the phylum Apicomplexa occurring in littoral or benthic invertebrates, especially amphipods. Gregarines are extracellular endoparasites of a broad range of invertebrates. Most of them inhabit host intestinal lumen and possess heteropolar elongated, cylindrical body with the anterior end attached to the host cells. Usually, the feeding stages of parasite (=trophozoites) are subdivided into three parts: epimerite (function of attachment), and protomerite followed by a deutomerite with large nucleus. The last two are separated by a fibrillar septum. Gregarines with such organisation represent the “tricystid” form of gregarines. On the other hand, the gregarines which are not subdivided represent the “monocystid” form. It should be also mentioned that, generally, trophozoites exhibit gliding motility and possess a unique organisation of cell cortex. The pellicle forms longitudinal epicytic folds with special sets of fibrils on the top. Before gametogenesis, the gamonts form a sexual association called syzygy. Later on, they round and form a common envelop (gametocyst), under which further process, including gametogenesis, fertilisation and formation of invasive stages (sporogenesis), take place (Desportes and Schrével 2013). Amphipods Gondogeneia sp. were collected on littoral of Cape Lachman, James Ross Island. Animals were dissected and gregarines were collected from their intestine with thin glass pipets. Parasites were measured, documented under light microscope, and fixed for electron microscopy. In the amphipod intestine we observed mostly syzygies, in which the partners contacted to each other in head-to-tail manner (Figure 1). The prevalence and abundance of parasite were very low: about 10% and 1-2 syzygy, correspondingly. Only few trophozoites were found. All found parasites showed similar morphology. Anterior gamont of syzygy (primite) was longer than posterior one (satellite). Both partners were of monocystid appearance and possessed oval or lentil-shaped nucleus, situated in the second half of the cell. The syzygies exhibited gliding motility. As other gregarines with this type of movement, the surface of observed gamonts was covered with longitudinal epicytic folds. The attachment site of the primite was convex with a crumpled surface, and epicytic folds extended from it towards the posterior end of the cell. The posterior end formed concave depression with a collar into which the anterior end of satellite plugged in. The cytoplasm of both gamonts was packed with amylopectin grains, which are the marker of gamont stage. So far, only two species of gregarines were reported from Antarctic region, from planktonic krill Euphasia superba and littoral amphipod Paramoera walkerii. Both of them belong to the family Cephaloidophoridae, which possess tricystid form of trophozoites and gamonts (Lipa and Rakusa-Suszczewski 1980, Takahashi et al. 2009). There numerous gregarines described from different crustaceans. Among them, the representatives of the family Ganymedidae are monocystid, parasitize in crustaceans, and in amphipods as well. They form a cup-like interface between the primite and satellite. We assume that newly found gregarine from Gondogeneia sp. belongs to this family (genus Ganymedes), but further investigations are needed.
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