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: Prymnesium radiatum Sym et al. 2011
Compiled data
Original Description
Size:
Etymology:
Extra details from original publication
Morphology of the colonies, cells and scales
Colonies of Prymnesium radiatum have a variable number of cells, usually 6–8 in exponentially growing cultures, but ranging from 2 to 20, with higher numbers (Fig. 5) more common in ageing cultures. Cultures rapidly collapse at the end of the exponential phase. The cells of colonies radiate out from a central point, with their flagellar poles outwardly directed (Figs 5, 7–9). Each cell is elongated and tapers to its base (Figs 1–5, 7–9) and has two chloroplasts (Fig. 6), which are golden. The chloroplasts are lobed (Fig. 6) both anteriorly, but particularly posteriorly (Figs 1–4) so that four long obviously discrete and ribbon-like lobes, not quite reaching the hyaline tail of the cell, can be distinguished. Cells are 7.4–19.3 µm long (average 12.0 µm) by 4.1–7.9 µm wide (average 6.4 µm). Cells usually actively beat their flagella, causing the entire colony to rotate while progressing, in a trembling fashion, through the water column. The sub-equal flagella (10.7–16.6 µm long; average 13.5 µm) are sub-apically inserted and beat homodynamically with a flagellar beat pattern. Inactive colonies are also common, particularly whilst being observed through a coverslip and, whilst in this state, the sub-equal flagella are held widely splayed (Figs 1–4) or with one flagellum tightly recurved alongside the body of the cell (not shown) or with both flagella tightly recurved along the surface of the cell, crossing over each other about midway down the length of the cell (lower cell, Figs 7–9). The haptonema (3.9–7.8 µm long; average 6.37 µm) is obvious, unbending, and anteriorly directed (Figs 3, 7) in both swimming and resting states. Cells of intact colonies are held together either by incomplete cytokinesis at the posterior ends of the cells (Figs 7–9) or, more frequently, by a mucilage-like extracellular matrix (Fig. 5). Individual cells of colonies trapped under a coverslip commonly rotate continually in one direction, yet still maintain their connection with the colony. Continual illumination with bright light during observation leads to the eventual dissociation of the cells. Colonies in actively growing cultures are well defined, but the cells of older colonies tend to dissociate.
Each cell possesses two types of organic scales (Figs 10–13). The smaller variety is typical for prymnesiophytes, with a small inflexed rim on the distal surface (Fig. 13). The proximal face is marked by radiating fibrils (Figs 11, 12) while the distal face has concentric fibrils (Fig. 13). The larger scale type is very distinctive for this species, having a base plate with the same patterning as the smaller scales but with an exaggerated, outwardly flexed rim, giving the overall morphology of the scale the semblance of a flowerpot (Figs 10, 11 and Sv in Figs 16, 19). No distal spines are subtended by the base plate.
Sym, S. D., Pienaar, R. N., Edvardsen, B. & Egge, E. S. (2011). Fine structure and systematics of Prymnesium radiatum sp. nov. (Prymnesiophyceae) from False Bay and Franskraal, South Africa. European Journal of Phycology. 46(3): 229-248. gs References:
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Prymnesium radiatum: Catalog entry compiled by Jeremy Young. Viewed: 17-2-2025
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