Original descriptions of taxa. For coccolithophores, and many calcispheres, these are pages from the Farinacci & Howe Catalog of Calcareous Nannofossils. In other cases (e.g. non-calcifying haptophytes) the data is directly compiled on this site. The "Catalogue of Calcareous Nannofossils" was originally compiled by Prof A. Farinacci 1969-1989, since 2000 it has been updated and extended by Richard Howe - see The Farinacci and Howe Catalog - an Introduction.
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Current identification/main database link: Dicrateria gilva Parke 1949
Compiled data
Original Description
Similar in form to the previous species [D. inornata], but shows several points of difference. The motile stage is larger, measuring 5-8 µm in diameter, and appears to have a slightly less rigid periplast (Text-figs. 63, 66). No stigma is developed, but two small non-contractile vacuoles, lacking in the previous species, are present near the point of origin of the flagella; the chromatophores are paler in colour and possess a faint greenish tinge (PI. I, fig. 3; Text-figs. 62-64).
The flagella, arising from one distant basal granule (or two adjacent granules), are three to four times the cell diameter in length and are therefore much longer than in the previous species; neither flagellum shows a plumate structure as far as could be seen from stained preparations. The movement of this organism differs also from that of D. inornata; there are alternate periods of movement and quiescence, but when swimming it shows fairly rapid movement with frequent change of direction. The position of the flagella when the cell is both in motion and at rest is the same as in D. inornata, but the flagella are more rigid when at rest than in the former species. This species is also phototactic in reaction.
Size:
Extra details from original publication
Asexual reproduction is by fission of the motile individuals and takes place as in D. inornata (Text-figs. 61, 65, 68). Stages in the formation of the cyst can be obtained from cultures 4-5 months old. The development of the cyst, inside the leucosin-filled cells, is the same as in Isochrysis galbana and Dicrateria inornata. The mature cysts are spheroidal or very slightly ovoid with a smooth silicified wall and a conical hyaline plug which is raised slightly above the surface of the cyst; they measure 7-7.5 µm in diameter. They are similar to that figured for D. inornata (Text-fig. 54), but are slightly larger. The release of the contents of the cyst has not been observed, but cysts from which the majority of the individuals had been released have been seen; the cells remaining in the cyst were ovoid and measured 4 µm in length.
Five of the six stages in the palmelloid form of reproduction, described in and figured for the two previous species, have been seen in this species. The first stage, measuring 6-7 µm in diameter, is spheroidal and shows two vacuoles and two or four chromatophores; in stage 2, the cells, covered by a thin gelatinous envelope, have four vacuoles, two nuclei and four or eight chromatophores; they measure. 9-10 µm in diameter. The large secondary envelope of stages 3 and 4 is not of such firm consistency as in the two previous species; it measures 18-20 µm in diameter. The free cells of stage 5 measure 4-5 µm, but stage 6, the escape of the contents of these cells, has not been observed.
Parke, M. (1949). Studies on marine flagellates. Journal of the Marine Biological Association of the United Kingdom. 28: 255-288. gsReferences:
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Dicrateria gilva: Catalog entry compiled by Jeremy Young. Viewed: 17-2-2025
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