Original descriptions of taxa. For coccolithophores, and many calcispheres, these are pages from the 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 compiled by Prof A. Farinacci 1969-1989 and updated by Richard Howe 2000-2016 - see also this page.
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Current identification/main database link: Dicrateria rotunda (Reynolds 1974) Bendif & Probert, in Bendif et al. 2013Compiled data
Cells motile, more or less spherical, 3-4 µm in diameter, not metabolic. Flagella two, smooth, homodynamic, 1-1½ cell diameters in length; haptonema not found. Two golden-brown parietal chloroplasts in younger cells, sometimes four or five in older cells, with embedded pyrenoids. Cell body bearing circular scales with coarse radial fibrils on their proximal faces; diameter approximately 0.5 µm
Size: Cells 3-4 µm; circular scales ca. 0.5 µm
Etymology: The name Imantonia was suggested by Dr M. Parke, in recognition of the very valuable contribution made by Professor Irene Manton, F.R.S., to our knowledge of the flagellates, and of the Haptophyceae in particular.
Extra details from original publication
Under the light microscope Imantonia is seen as a small, more or less spherical organism bearing two equal flagella. When it is swimming actively the flagella are behind the cell, and roughly parallel to each other. In this condition a cell may traverse the microscope field with little change of direction. When swimming slowly, and more erratically, the flagella appear to be in front of the cell and quite divergent. The type culture was actively motile when isolated, but became less so on prolonged subculturing. Full motility was restored by growing it for a short time in a tube with soil on the bottom, covered by a thin layer of agar, and with the usual culture solution above. The addition of soil extract to the culture solution did not have the same effect.
The cells are golden-brown in colour and, although they lack a definite cell wall, they are not metabolic. Characteristic appearances of cells at rest are shown in Figs 3 and 4. The chloroplasts, usually two, but sometimes four or five in older cells, are parietal. Under the electron microscope they are seen to have the usual haptophycean lamellar structure with three thylakoids per lamella, except in the pyrenoids, where the thylakoids are reduced to two per lamella (Fig. 6). No stigma has been seen. The nucleus is fairly large, irregularly shaped, and situated either medianly in the cell or towards the end opposite to the flagellar bases. It is bounded by the usual double membrane with nuclear pores. The nucleolus is normally clearly differentiated (Fig. 2). The Golgi body is visible in suitable sections as a stack of dome-shaped cisternae near the bases of the flagella, and situated between them and the nucleus. The "peculiar" thickenings described by Manton (1967) for some other members of the Haptophyceae are clearly visible (Fig. 2). The formation of scales within the Golgi body has also been seen.
The two smooth flagella arise close together (Figs 2-5) and are equal or sub-equal in length (3-7 µm); the tips are tapered and smoothly rounded at the ends. At rest the flagella project from the cell, diverging at about 90-120 °, straight or slightly curved. Serial sections through the flagellar pole of the cell have failed to reveal any evidence of the presence of a haptonema.
The body scales are of a characteristic type resembling bicycle wheels, with a delicate rim and 17-20 spokes radiating from a central point (Fig. 7). The base is extremely delicate and ornamented with a very fine pattern of markings linking the spokes and producing the effect of a fine cobweb. The width of the rim of the scales varies from about 20 nm to 100 rim. In shadowcast preparations the rim may collapse and lie in the plane of the base, but it is apparent from the examination of sections that it extends perpendicularly to the plane of the scale, and presumably away from the body of the organism. Although scales appear at times to be present in large numbers, it has proved to be extremely difficult to get a picture showing a scale in position on the cell body.
Reserve materials are stored as leucosin. Staining with cresyl blue commonly reveals two or three leucosin vesicles towards the end of the organism opposite to the flagellar pole. They are clearly visible under the light microscope, and show in sections under the electron microscope as round bodies up to 1µm in diameter, with uniform contents which stain moderately.
The remaining structures of interest in the cells are vesicles of about the same size as the leucosin vesicles, which sometimes contain a background material staining similarly to leucosin, but which also contain a collection of globules and membranes similar to those reported by Belcher & Swale (1971) for Phaester pascheri Scherffel.
Reproduction has not so far been observed, apart from one cell which bore four flagella emerging close together. This may have been about to divide longitudinally.