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Gymnodinium veneficum Ballantine, 1956

Species Overview:

Gymnodinium veneficum is an unarmoured, marine, planktonic dinoflagellate species. This small species has been associated with fish and shellfish mortality events.

Taxonomic Description:

Gymnodinium veneficum is an athecate species; i.e. without thecal plates. Cells are small and ovoid without dorso-ventral compression (Figs. 1-3). Cells range in size from 9-18 µm in length to 7-14 µm in width (Ballantine, 1956, Dodge, 1982, Taylor et al., 1995).

The epitheca and hypotheca are equal in size. The cell's anterior end is slightly pointed; the epitheca is without an apical groove. The hypotheca is rounded with a slight indentation at its posterior end. The deep cingulum is displaced in a descending spiral 1-2 times its width. The sigmoid sulcus slightly invades the epitheca (Figs. 1-3) (Ballantine, 1956, Dodge, 1982, Taylor et al., 1995).

Morphology and Structure:

G. veneficum is a photosynthetic species and usually has four irregularly shaped, golden-brown chloroplasts with pyrenoids; occasionally two to eight are present. The large round nucleus is centrally located (Figs. 2,3) (Ballantine, 1956, Dodge, 1982, Taylor et al., 1995).


G. veneficum reproduces asexually by binary fission; cells divide obliquely during mitosis (Ballantine, 1956).

Species Comparison:

In general cell shape and size, G. veneficum can easily be mistaken for G. micrum, a non-toxic species. However, the former species usually has four chloroplasts present and is toxic to invertebrates and fish (Taylor et al., 1995).


G. veneficum is a planktonic species first described from the English Channel (Ballantine, 1956).


G. veneficum is a known toxic species; it produces an exotoxin lethal to a wide variety of invertebrates and fish (Ballantine, 1956, Abbott and Ballantine, 1957, Dodge, 1982).

Habitat and Locality:

G. veneficum was described from the English Channel. It may be a wide-spread species, but due to its minute size, it most likely has been greatly overlooked in phytoplankton assessments (Ballantine, 1956, Dodge, 1982).

Gymnodinium veneficum