Gymnodinium pulchellum Larsen, 1994
Species Overview:
Gymnodinium pulchellum is an unarmoured, marine, planktonic dinoflagellate species. This species produces red tide blooms and has been associated with fish and invertebrate kills in Japan and Florida.
Taxonomic Description:
Gymnodinium pulchellum is an athecate species; i.e. without thecal plates. Cells are small and broadly oval with slight dorso-ventral compression (Figs. 1-6). The ventral surface is flattened; the dorsal surface is rounded. A conspicuous and well-defined sigmoid apical groove is present on the epitheca (Fig. 1); the groove is a characteristic reversed S-shape (Fig. 2). Cells range in size from 16-25 µm in length to 11-16 µm in width (Fukuyo et al., 1990, Larsen, 1994, Taylor et al., 1995, Steidinger and Tangen, 1996, Steidinger et al., 1998).
The epitheca is slightly smaller than the hypotheca. The wide and deeply excavated cingulum is premedian, and is displaced in a descending fashion 1-1.5 times its width (Figs. 1,3,4). The sulcus invades the epitheca slightly as a finger-like projection (Fig. 2). The sulcus widens and deepens towards the posterior of the cell creating a bilobed hypotheca (Figs. 1,3,4) (Larsen, 1994, Taylor et al., 1995, Steidinger and Tangen, 1996, Steidinger et al., 1998).
Morphology and Structure:
G. pulchellum is a photosynthetic species with several yellowish-brown chloroplasts. Pyrenoids are also present (Figs. 3,4). The large nucleus is ellipsoidal and located in the left part of the cell (Figs. 5,6) (Fukuyo et al., 1990, Larsen, 1994, Steidinger and Tangen, 1996, Steidinger et al., 1998).
Reproduction:
G. pulchellum reproduces asexually by binary fission.
Species Comparisons:
Sharing the same habitat and locale, and the same general shape, G. pulchellum can be confused with G. mikimotoi. G. pulchellum, however, is smaller in size and has a distinctive sigmoid apical groove; the apical groove of G. mikimotoi is straight (Larsen, 1994).