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Dinophysis rotundata Claparède and Lachmann, 1858-1859

Species Overview:

Dinophysis rotundata is an armoured, marine, planktonic dinoflagellate species. It is a toxic heterotrophic species widely distributed in cold and warm 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 Dinophysis rotundata are medium-sized and broadly rounded in lateral view with convex ventral and dorsal margins (Figs. 1-6). Left sulcal list extends over 1/2 to 3/4 of cell length (Figs. 1-3). The greatest dorso-ventral width is between the base of the second and third rib of the left sulcal list (Fig. 2) (Lebour, 1925, Abè, 1967, Balech, 1976, Dodge, 1982, Larsen and Moestrup, 1992, Steidinger and Tangen, 1996).

Thecal surface is covered with poroids and scattered pores (Figs. 1,2,5,6). Cell size ranges: 36-56 µm in length and 36-43 µm in dorso-ventral width (Lebour, 1925, Balech, 1976, Dodge, 1982, Taylor et al., 1995, Steidinger and Tangen, 1996).

Thecal Plate Description:

The epitheca in this species is visible in lateral view; it is a small convex cap above the cingulum, low and fairly evenly rounded (Figs. 1-3,6) (Abè, 1967, Balech, 1976, Dodge, 1982, Larsen and Moestrup, 1992, Taylor et al., 1995). It is made up of four plates coarsely areolated (Figs. 1,2,6) (Lebour, 1925).

The cingulum bears two narrow well developed lists: an anterior cingular list (ACL), and a posterior cingular list (PCL) (Figs. 1,2,6). The lists are smooth, but sometimes with surface ornamentation. Both lists incline anteriorly; however, the ACL does not entirely obscure the epitheca (Lebour, 1925, Balech, 1976, Dodge, 1982, Larsen and Moestrup, 1992, Taylor et al., 1995).

The sulcus is comprised of several irregularly shaped plates. The flagellar pore is housed in the sulcal area. The left sulcal list (LSL), supported by three ribs, is relatively narrow often widening posteriorly (Figs. 1-3,6). The first two ribs are spaced closer together than the second and third ribs (Figs. 2,6). Narrower than the LSL, the right sulcal list (RSL) is relatively long, reaching or slightly posterior to the third rib of the LSL (Figs. 1,6) (Lebour, 1925, Balech, 1976, Dodge, 1982, Taylor et al., 1995).

The hypotheca, with four large plates, comprises the majority of the cell. The ventral margin is almost straight to slightly convex between the first and third LSL ribs (Figs. 2,6). The dorsal margin is much more convex (Figs. 1,2,6). Posterior region rounded (Figs. 1-6) (Balech, 1976).

Morphology and Structure:

Dinophysis rotundata is a heterotrophic species without chloroplasts, and with a posteriorly oriented nucleus (Fig. 4). The protoplasm is clear with numerous food vacuoles (Fig. 3). Megacytic stages frequently observed (Lebour, 1925, Balech, 1976, Dodge, 1982, Larsen and Moestrup, 1992).

Reproduction:

D. rotundata reproduces asexually by binary fission.

Species Comparison:

Dinophysis rotundata looks similar to D. rudgei (or Phalacroma rudgei), however, the latter species has a more prominently visible epitheca and is also a larger species (Taylor et al., 1995, Steidinger and Tangen, 1996).

Remarks:

Many authors consider Dinophysis to be synonymous with Phalacroma (Steidinger and Tangen, 1996).

Ecology:

D. rotundata is a planktonic species. No blooms have been reported for this species (Lebour, 1925, Balech, 1976, Dodge, 1982, Larsen and Moestrup, 1992). This heterotrophic species feeds phagotrophically: it feeds on loricated and non-loricated ciliates and picoplankton (Faust, M.A., unpublished) which are ingested via a peduncle (Hansen, 1991, Inoue et al., 1993).

Toxicity:

Dinophysis rotundata is a toxic species producing the DSP toxin dinophysistoxin-1 (DTX1). This is the first heterotrophic dinoflagellate in which toxin production has been demonstrated (Lee et al., 1989). However, only Japanese strains of this species have been found to produce the toxins; North American strains have proved non-toxic (Cembella, 1989).

Habitat and Locality:

Dinophysis rotundata is a cosmopolitan species widely distributed in cold and warm waters (Larsen and Moestrup, 1992, Taylor et al., 1995, Steidinger and Tangen, 1996).

Dinophysis rotundata