Dinophysis rotundata

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species feeds phagotrophically: it feeds on loricated and non-loricated ciliates and picoplankton (Faust, M.A., unpublished) which are ingested via a peduncle (Hansen 1991; Inoue et al. 1993).

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

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

Holotype: Dinophysis rotundata Claparède and Lachmann, 1859: 6, plate 20, fig. 16
Type Locality: North Sea: Glesnesholm, Norway

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

D. rotundata reproduces asexually by binary fission.

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 & Tangen 1996).

Dinophysis rotundata is an armoured, marine, planktonic dinoflagellate species. It is a toxic heterotrophic species widely distributed in cold and warm waters.

Phalacroma rotundatum Kofoid and Michener, 1911
Dinophysis whittingae Balech, 1971a

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. 1-4). Left sulcal list (LSL) extends over 1/2 to 3/4 of cell length (Figs. 2-4). Greatest dorso-ventral width is between the base of the second and third rib of the LSL (Figs. 2,3)(Lebour 1925; Abè 1967; Balech 1976; Dodge 1982; Larsen & Moestrup 1992; Steidinger & Tangen 1996).
Thecal surface is covered with poroids and scattered pores (Figs. 1, 2). 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 & Tangen 1996).

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, 3-5) (Abè 1967; Balech 1976; Dodge 1982; Larsen & Moestrup 1992; Taylor et al. 1995). It is made up of four plates, coarsely areolated (Lebour 1925).
The cingulum bears two narrow well developed lists: an anterior cingular list (ACL), and a posterior cingular list (PCL) (Figs. 1,5). The lists are smooth, but may have ornamentation. Both lists incline anteriorly without entirely obscuring the epitheca (Fig. 1)(Lebour 1925; Balech 1976; Dodge 1982; Larsen & 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 LSL, supported by three ribs, is relatively narrow, often widening posteriorly (Figs. 2,5). The first two ribs are spaced closer together than the second and third ribs (Figs. 2, 3, 5). Narrower than the LSL, the right sulcal list (RSL) is relatively long, reaching or slightly posterior to the third rib of the LSL (Fig. 2) (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. 3, 5). The dorsal margin is much more convex (Figs. 3, 4). Posterior region rounded (Figs. 1-4) (Balech 1976).

Dinophysis rotundata is a toxic species producing the diarrhetic shellfish poison (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).