Ultrastructure of trichocysts in Hematodinium spp. infecting Atlantic snow crab, Chionoecetes opilio

Ultrastructure of Selected Life History Stages of the Parasitic Dinoflagellate Euduboscquella cachoni

Euduboscquella species differ from most other syndinean dinoflagellates by having mononucleate trophonts, but resemble species of Amoebophrya and Sphaeripara by episome-hyposome differentiation and cortical complexity. Cytology and development of Euduboscquella species are well characterized, but their ultrastructure remains essentially unexplored. Transmission electron microscopy of Euduboscquella cachoni trophonts, tomont, and sporocytes revealed previously unrecognized structures. Initially dense, fibrous chromosomes uncoiled during early infection, with condensed chromosomes absent over much of the growth cycle recondensing at trophont maturity. The hyposomal amphiesma was two appressed membranes, the episomal cortex was alveolate, and a supraepisomal cavity limited by membrane enclosed the episome. Pseudopod-like extensions of the hyposome during mid infection may facilitate osmotrophic nutrition. The pharyngeal lamina appears to lack ingestatory function; however, transcortical transport of particles occurred via the supraepisomal cavity and episomal micropores. Microtubules originating from the electron-opaque perinema bordering the episome, formed an episomal skeleton hypothesized to function with the pharyngeal lamina, perinema, and the paired membranes of the supraepisomal cavity to effect parasite egress and ingestion of host material. Trichocysts absent during early infection developed during late infection and reached maturity during sporogenesis, suggesting functional importance in spore survival or infection.

In vitro cultivation of Hematodinium sp. isolated from Atlantic snow crab, Chionoecetes opilio: partial characterization of late developmental stages

Hematodinium is a parasitic dinoflagellate of numerous crustacean species, including the economically important Atlantic snow crab, Chionoecetes opilio. The parasite was cultured in vitro in modified Nephrops medium at 0 °C and a partial characterization of the life stages was accomplished using light and transmission electron microscopy (TEM). In haemolymph from heavily infected snow crabs two life stages were detected; amoeboid trophonts and sporonts. During in vitro cultivation, several Hematodinium sp. life stages were observed: trophonts, clump colonies, sporonts, arachnoid sporonts, sporoblasts and dinospores. Cultures initiated with sporonts progressed to motile dinospores; however, those initiated with amoeboid trophonts proliferated, but did not progress or formed schizont-like stages which were senescent artefacts. Plasmodial stages were associated with both trophonts and sporonts and could be differentiated by the presence of trichocysts on TEM. Macrodinospores were observed but not microdinospores; likely due to the low number of Hematodinium sp. cultures that progressed to the dinospore stage. No early life stages including motile filamentous trophonts or gorgonlocks were observed as previously noted in Hematodinium spp. from other crustacean hosts. All Hematodinium sp. life stages contained autofluorescent, membrane-bound electron dense granules that appeared to degranulate or be expelled from the cell during in vitro cultivation.