Fine structure and biology of Cryothecomonas gen. nov. (Protista incertae sedis) from the ice biota

Abstract

1991. Fine structure and biology of Cryothecomonas gen.nov. (Protista incertae sedis) from the ice biota. Can. J. Zool. 69: 1048-1070. The morphology and ultrastructure of four species of Cryothecomonas gen.nov. (Protista incertae sedis) in material from the Weddell Sea, Antarctica, and the Isefjord, Denmark, are described. These heterotrophic flagellates, which were initially observed in association with sea ice, display a unique combination of morphological characteristics. At present it is impossible to assign the new genus to an existing higher taxonomic level of protistan flagellates. Cryothecomonas species are furnished with a close-fitting multilayered theca. The two naked anterior flagella emerge through narrow thecal funnels. A transitional helix is part of the flagellar transition zone. A conspicuous cytostome is located in a posterior (lateral) position. Food uptake is mediated through the extension of cytostomal pseudopodia. The nucleus is anteriorly located and contains a conspicuous nucleolus and distinct areas of chromatin. Mitochondria1 cristae are tubular. Cryothecomonas species feed on cells in the size range 2-4.5 k m (e.g., algal flagellates). Data are presented on the abundance of Cryothecomonas armigera sp.nov. in Antarctic waters.

Cryothecomonas aestivalis sp. nov., a colourless nanoflagellate feeding on the marine centric diatomGuinardia delicatula (Cleve) Hasle

“…We studied the vegetative hfe cycle of this flagellate, especially its mode of food uptake, and its ultrastructure. As a result our new flagellate is assigned to the genus Cryothecomonas, which has recently been described by Thomsen et al (1990). C. aestivalis sp.…”

“…Unlike Thomsen et al (1990), we had mainly trophontic and subsequent reproductive stages inside the diatom frustule at our disposal. Nevertheless, many characters of C. aestivalis are completely or largely identical with those of the four species described by Thomsen et al (1990), which also differ from one another in some details.…”

“…In the basal region of the trophonts, where the food is phagocytized, the theca has a gap. The cell periphery consists here of a labyrinth of cytoplasmic processes and invaginations -the cytostome in the terminology of Thomsen et al (1990) (Fig. 20).…”

“…More apically the satellites are arranged in the form of a cylinder or cone. Some of them are connected by radial strands ("transitional fibres" sensu Thomsen et al, 1990) with the triplets of the basal body (Figs 28,29). A microtubular flagetlar root originates in the region where the two basal bodies lie close together (Figs 26,32, and the scheme, Fig.…”

“…The two apically inserted flagella are heretodynamic and of unequal length. They are smooth, and their basal bodies are surrounded by satellites and fibrous strands ("transitional fibres" sensu Thomsen et al, 1990). In the trophonts and dividing flagellates the transition region between the flagellum and the basal body ends apically with a massive transitional cylinder instead of distinct microtubules, and is surrounded by a funnel of the theca.…”