Dinophysis mitra (Schütt) Abè, 1967a
Species Overview:
Dinophysis mitra is an armoured, marine, planktonic dinoflagellate species. It is a toxic species widely distributed in warmer waters.
Taxonomic Description:
Species in this genus are laterally compressed with a small, cap-like epitheca and a much larger hypotheca (dorso-ventral depth of epitheca is 1/2 to 2/3 of hypotheca). The shape of the cell in lateral view is the most important criterion used for identification (Taylor et al., 1995).
Cells of D. mitra are large, broad and wedge-shaped (Figs. 1-3). The ventral hypothecal margin is distinctly concave below the left sulcal list (LSL) (Figs. 1-3). The LSL is relatively short, only half of the total cell length (Figs. 1-3). This species is widest at the base of the second rib of the left sulcal list (Figs. 1-3) (Larsen and Moestrup, 1992, Taylor et al., 1995, Steidinger and Tangen, 1996).
The theca are thick and coarsely areolated (Figs. 1-3). Areolae are large; some with a small central pore (Fig. 6). Cell size ranges: 70-95 µm in length and 58-70 µm in dorso-ventral width (at base of second rib of LSL) (Larsen and Moestrup, 1992, Taylor et al., 1995).
Thecal Plate Description:
The small epitheca is slightly convex, appearing as a cap above the cingulum. The four epithecal plates are coarsely areolated (Figs. 2,4). The anteriorly situated cingulum has two narrow, well developed lists, anterior cingular list (ACL) and posterior cingular list (PCL), supported by many ribs (Figs. 2,5,6). The sulcus is comprised of several irregularly shaped plates (Fig. 6). The flagellar pore is housed in the sulcal area. The short LSL is supported by three short ribs (Figs. 2,3,7,8) (Larsen and Moestrup, 1992, Taylor et al., 1995).
The hypotheca, with four large plates, comprises the majority of the cell. The dorsal margin is smoothly convex (Figs. 1-3). The ventral margin is more or less straight in the sulcal region, becoming distinctly concave at the posterior end of the LSL towards the antapex of the cell (Figs. 1,3). As the megacytic zone expands during cell growth, the posterio-ventral concavity of the hypotheca becomes much less distinct (Larsen and Moestrup, 1992, Taylor et al., 1995).
Morphology and Structure:
Dinophysis mitra is a photosynthetic species with chloroplasts (Schütt, 1895).
Reproduction:
D. mitra reproduces asexually by binary fission.
Species Comparison:
Dinophysis mitra resembles D. rapa; Schiller, 1933 stated that the two species are probably synonymous. The two species can be distinguished by D. rapa's stronger protuberant sulcal ridge at the base of the third rib of the LSL (left ventral margin is angled), and its extreme concavity of the hypothecal posterior ventral margin. D. rapa is also a larger species (Abè, 1967a, Larsen and Moestrup, 1992, Steidinger and Tangen, 1996).
Remarks:
Many authors consider Phalacroma to be synonymous with Dinophysis (Steidinger and Tangen, 1996).