Gymnodinium breve Davis, 1948
Species Overview:
Gymnodinium breve is an unarmoured, marine, planktonic dinoflagellate species. It is a toxin-producing species associated with red tides in the Gulf of Mexico, off the coast of western Florida.
Taxonomic Description:
Gymnodinium breve is an athecate species; i.e. without thecal plates. Cells are small and dorso-ventrally flattened (Figs. 1,2). The cell is ventrally concave and dorsally convex. Cells appear almost square in outline, but with a prominent apical process directed ventrally (Figs. 1-3). Cells range in size from 20-40 µm in width to 10-15 µm in depth, and is slightly wider than long (Steidinger et al., 1978, Steidinger, 1983, Taylor et al., 1995, Steidinger and Tangen, 1996).
The epitheca is rounded with a distinctive overhanging apical process (Figs. 1,2). The epitheca is smaller than the hypotheca (Fig. 1). The cingulum is displaced in a descending fashion up to 2 times its width. It houses the transverse flagellum. The sulcus extends into the epitheca up to the apex adjacent to the apical process (Fig. 3). It houses the longitudinal flagellum. An apical groove, present near the distal epithecal end of the sulcus, extends across the apical process onto the dorsal side of the cell (Figs. 1,3). It is not an extension of the sulcus. The wide hypotheca is notched by the sulcus and is slightly bilobed posteriorly. Discharged trichocysts have been observed (Davis, 1948, Steidinger et al., 1978, Steidinger, 1983, Taylor et al., 1995, Steidinger and Tangen, 1996).
Morphology and Structure:
Gymnodinium breve is a photosynthetic species with numerous peripheral yellowish-green chloroplasts and multistalked pyrenoids. The large round nucleus is 6-9 µm in diameter and located in the left half of the hypotheca (Figs. 2,3). Lipid globules have also been observed. This species does not have peridinin as a major accessory pigment (Davis, 1948, Steidinger et al., 1978, Steidinger, 1983, Taylor et al., 1995, Steidinger and Tangen, 1996).
Reproduction:
G. breve reproduces asexually by binary fission; cells divide obliquely during mitosis. This species also has a sexual cycle: isogamous gamete production, fusion and formation of a planozygote. The planozygote is morphologically similar to the vegetative cell, but larger. The gametes are rounder and slightly smaller than the vegetative cells (18-24 µm in diameter). It is speculated that temperature controls the onset of the sexual cycle since sexual stages only occurred in fall and winter in both field populations and cultures (Walker, 1982).