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 inornata Parke 1949
Compiled data
Original Description
The motile stage is spheroidal to slightly ovoid, and possesses a rather rigid undifferentiated periplast, which does not admit of any change of shape. In the young motile stage, two large saucer-shaped chromatophores, golden- brown in colour, are normally present; they are parietal and opposite in position so that a clear zone of cytoplasm lies between them (PI. I, fig. 1; Text-fig. 51). In the older motile stage four chromatophores are more frequently developed (Text-figs. 48, 52). The medium-sized nucleus is situated near to the pole from which the flagella arise and in the young stage a rather small mass of leucosin is present at the opposite pole (PI. I, fig. 1). Small oil drops are distributed through the general cytoplasm, but the species lacks both stigmata and vacuoles.
Two equal flagella, one and a half to twice the diameter of the cell in length, arise from a distinct basal granule, or from two placed very close together, situated in the clear part of the cytoplasm (Text-figs 46, 48); they are very delicate, but can just be seen in the living cells. Stained preparations show that both flagella taper very slightly towards the free end, and neither are apparently plumate in structure. When in motion the cells rotate in a slow and steady manner and are constant in direction for relatively long periods. When swimming the flagella lie backwards down the sides of the body and carry out an undulating movement, but when at rest, they lie away from the body. Before the swimming individuals come to rest, however, they exhibit, for a short time, a peculiar dithering movement; they then remain motionless for a fairly long period. This species is slightly phototactic in reaction.
Size:
Extra details from original publication
Asexual reproduction by division of the motile cells takes place in both the light and the dark. Counts show that more than two divisions can take place within 6 hr. The procedure is similar to that described in Isochrysis. When about to divide the cell broadens, the two chromatophores divide, if they have not already divided, and the leucosin breaks up into two or more smaller masses. The nucleus then divides and the two flagella separate, each attached to its basal granule or part of the basal granule (Text-fig. 49). Fission of the cell starts at the pole from which the flagella arise and passes down through the individual until the two cells are connected only at the pole away from the flagella (Text-fig. 50). A second flagellum is developed by each daughter- cell before they finally separate; the cells are usually of equal size. No loss or withdrawal of the flagella before fission has been observed in this species.
Cyst formation occurs in cultures left 5 months without subculturing. The cysts develop inside the leucosin-filled cells (Text-fig. 53) in a manner similar to that described for Isochrysis. The mature cysts are spheroidal with a smooth silicified wall and a plug, the shape of a truncated cone, that is raised slightly above the general surface of the cyst (Text-fig. 54).
The form of reproduction in the palmelloid phase found in the genus Isochrysis occurs also in this genus. In Dicrateria inornata the six stages in the cycle denned earlier have been obtained from old cultures (Text-figs. 55- 60). The large spheroidal, leucosin-filled cells of stage 1 measure 4-5-5 µm (Text-fig. 55); stages in the apparent fusion of pairs of these cells have been seen, but the actual fusion of the nuclei of the cells has not yet been observed. Stage 2, the larger binucleate cell covered by a thin gelatinous envelope, has been found frequently (Text-fig. 56); it measures 7-8 µm in diameter. Stage 3, the uninucleate cell (Text-fig. 57), and stage 4, the division of this cell into four daughter-cells (Text-fig. 58), are not uncommon; the large secondary gelatinous envelope surrounding these stages measures 15-17 µm in diameter. In stage 5 the four daughter-cells become free by the disintegration of the large gelatinous envelope: they are spheroidal and are covered by a very thin, smooth, firm wall, measuring about 3 µm in diameter (Text-fig. 59). Stage 6, the liberation of the contents of these cells, has also been seen; the contents escape from a small pore as a single small individual of the motile stage, measuring approximately 3 µm in diameter (Text-fig. 60).
D. inornata shows some resemblance to Chrysidalis peritaphrena Schiller, but it is smaller and lacks the decided groove, passing forwards and backwards from the base of the flagella, which is present in that species.
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 inornata: Catalog entry compiled by Jeremy Young. Viewed: 17-2-2025
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