Cryothecomonas
Cryothecomonas (Protista incertae sedis) Thomsen, Buck, Bolt & Garrison (ref. ID; 5768 original paper)
See Protaspis
[ref. ID; 5694]
Circumscription; Biflagellated heterotrophic flagellate moving by swimming or gliding, with one anteriorly directed and one posteriorly directed flagellum, body surface coated in delicate theca except at site of emergence of flagella and in area of food ingestion. Theca not visible by light microscopy. Feeding by ingestion by ventral face of body often involving pseudopodia. (ref. ID; 5694)
Ultrastructural identity; Mitochondria with tubular cristate, two flagella inserting as inclined basal bodies interconnected by a striated band, giving rise to several microtubular arrays, one of which links basal bodies to nucleus, transition zone with constriction, cell with dictyosomes and osmiophilic bodies. Cell surface with thin organic coating. During mitosis, the nuclear envelope disintegrates, spindle microtubules arise from basal bodies. (ref. ID; 5694)
Synapomorphy; Not specified - this is a tubulocristate flagellate with body enclosed by delicate mucoid theca and a large ventral groove, but neither feature is unique to this taxon. (ref. ID; 5694)
Composition; One genus, several species. (ref. ID; 5694)
References; Thomsen et al. 1991; Drebes et al. 1996. (ref. ID; 5694)
[ref. ID; 5768]
Diagnosis; Protists enclosed in close-fitting theca with sharply defined funnels and cytostomal regions through which emerge the two flagella and the pseudopodia, respectively. The flagella are without hairs or scales. A transitional helix is present above the distal transverse partition. Electron-dense bodies (50-80 nm in diameter) occur at the extreme anterior end of the cell. Flagellar basal bodies make close contact with the anteriorly located large nucleus, which is characterized by a large nucleolus and areas of permanently condensed chromatin. Mitochondria have tubular cristae. Extrusomes and muciferous bodies are commonly present. Phagotrophic feeding is by means of pseudopodia emerging through a cytostomal slit. Lysosome-like bodies are abundantly present. Division is by means of longitudinal fission of flagellated cells. The plane of division is perpendicular to the shortest axis of the cell, thus splitting the cytostomal groove. (ref. ID; 5768)
Etymology; The tripartite generic name reflects three characteristic features of this taxon: its association with sea ice (cryo), the presence of a protective coat outside the plasmalemma (theca), and its morphological type (monad, i.e., a single cell with flagella). (ref. ID; 5768)
Type species; Cryothecomonas armigera (ref. ID; 5768)
- Cryothecomonas armigera Thomsen, Buck, Bolt & Garrison (ref. ID; 5768 original paper)
- Cryothecomonas inermis Thomsen, Buck, Bolt & Garrison (ref. ID; 5768 original paper)
- Cryothecomonas scybalophora Thomsen, Buck, Bolt & Garrison (ref. ID; 5768 original paper)
- Cryothecomonas vesiculata Thomsen, Buck, Bolt & Garrison (ref. ID; 5768 original paper)
Cryothecomonas armigera Thomsen, Buck, Bolt & Garrison (ref. ID; 5768 original paper)
Diagnosis
Cells egg-shaped and dorsoventrally flattened (12-32 x 7-23 x ca. 5 um). The cytostome is located at the posterior end of the cell at the bottom of a lateral groove. The theca is multilayered, with an electron-dense inner layer and an outermost layer in which the material is arranged to form regularly spaced ridges. Extrusomes are present throughout the cell. (ref. ID; 5768)
Descriptions
- Light microscopy: Living cells of C. armigera are difficult to observe under the light microscope unless the microscope stage is maintained at a temperature close to 0 degrees C. When examined in an ordinary wet preparation the cells do not move much, although some are observed to beat both flagella vigorously immediately upon transfer from the culture vessel to the microscope. The pattern of movement of the isodynamic flagella is generally similar to that observed in species of the green algal flagellate Chlamydomonas, although in C. armigera the flagellar beat is more irregular. In some cells one flagellum was occasionally at rest while the other was still in mortion. It is unclear whether this is a reaction to the stressed conditions or a result of the flagella not being completely isodynamic. Most of the cells observed from cultures were egg-shaped and markedly flattened. In all preparations some cells were irregular in outline and either slightly twisted or with conspicuous cell surface foldings. The papilla, the anteriorly positioned nucleus with a conspicuous nucleolus and condensed chromatin, and food vacuoles or lipid droplets are structures that are easy to observe under the light microscope. Cells of C. armigera fix well in Lugol's solution. Details of the cytostome become more visible once the cells are fixed. Several short pseudopodia are present in the cytostomal regions of the cells. The discharge of extrusomes is a natural reaction against the fixation of the cells. The maximum length of these filamentous structures is approximately 10 um. The presence of a protective coat ("theca") outside the plasmalemma can be difficult to verify using light microscopy. It is evident that the cell surface prossesses some kind of rigidity indicative of the presence of supporting layers in addition to the plasmalemma. That this is in fact a theca (separate from the cell) and not a cell wall (cf. the cholorophycean genus Clamydomonas) or pellicle (cf. the euglenophycean genus Eutreptiella) is generally only clear in cells in which the cytostome is visible. According to our experience this is the only cell surface area in which, owing to high activity of the underlying cytoplasm, the theca sometimes becomes pushed so far away from the plasmalemma that it actually becomes visible as a separate unit. (ref. ID; 5768)
- Scanning electron microscopy: The cells are flattened and tend to settle, exposing the broad, elliptical cell outline. Two almost equal, naked flagella emanate through funnels located at the base of an anterior papilla. The flagella in most cases equal the cell body in length. However, in a few cells examined in the SEM the flagella were twice the length of the cell. A curled-up flagellar tip observed in most specimens is believed to be an artifact (perhaps a fixational modification of a flagellar hairpoint). Despite the critical-point drying of the material and careful handling of the cells during processing, the protective coat on the outside of the cell was somewhat damaged. The ruptured layer probably represents the outermost striated thecal layer. The large number of intracellular spherical bodies located next to the plasmalemma, sometimes causing local out-bulgings of the cell, are almost certainly food vacuoles or lipid droplets. All cells examined in the SEM possessed a characteristic longitudinal furrow along one narrow side of the cell. The length of this furrow varies. In most cells it runs from the posterior tip of the cell to the midregion. In some cells the furrow is visible almost to the anterior end. A conspicuous cytostome, an elongated slit-like aperture, is located at the posterior end of the furrow. Through this structure food particles are engulfed and presumably waste material is discarded. The irregular and unfolded material visible through the cytostomal opening may represent the tips of numerous contracted pseudopodia. The photograph of feeding cell is evident that veil-like pseudopodia, emanating through the cytostomal slit, have encircled one ends of a pennate diatom (Nitzschia cylindrus). Discharged extrusomes measure approximately 0.2 um in width. After discharge they remain attached at one end to the cell surface (theca). (ref. ID; 5768)
Etymology
armigera (Latin) means "carrying weapons" (extrusomes here). (ref. ID; 5768)
Type locality
Weddell Sea, Antarctica, June 1988. (ref. ID; 5768)
Cryothecomonas inermis Thomsen, Buck, Bolt & Garrison (ref. ID; 5768 original paper)
Diagnosis
Similar to C. armigera, but smaller (10-15x7-10 um), less conspicuously dorsoventrally flattened, and without extrusomes. (ref. ID; 5768)
Etymology
inermis (Latin) means "without weapons" (extrusomes here). (ref. ID; 5768)
Type locality
The Isefjord, Denmark. Material collected 12 February 1985 from underneath sea ice. (ref. ID; 5768)
Cryothecomonas scybalophora Thomsen, Buck, Bolt & Garrison (ref. ID; 5768 original paper)
Diagnosis
Cells variable in shape (9-14x4.5-9 um). The theca consists of a single electron-dense layer which externally supports regularly spaced protuberances. Cells surrounded by debris outside the theca. A few large extrusomes are present at the anterior end of the cell. Complex pseudopodia emanate from the cytostome. (ref. ID; 5768)
Etymology
The species name is derived from scybalon (Greek) and phora (Greek) and means "to carry garbage". (ref. ID; 5768)
Type locality
The Isefjord, Denmark. Material collected 12 February 1985 from underneath sea ice. (ref. ID; 5768)
Cryothecomonas vesiculata Thomsen, Buck, Bolt & Garrison (ref. ID; 5768 original paper)
Diagnosis
Cells are elongate (9-14x4.5-9 um). The theca consists of two distinct layers. Muciferous bodies are regularly packed (hexagonal close packing) underneath the entire cells surface. Lysosome-like bodies very conspicuous. (ref. ID; 5768)
Etymology
The epithet refers to the multitude of muciferous bodies (vesicles). (ref. ID; 5768)
Type locality
The Isefjord, Denmark. Material collected 12 February 1985 from underneath sea ice. (ref. ID; 5768)