Dinophysis tripos Gourret, 1883
Species Overview:
Dinophysis tripos is an armoured, marine, planktonic dinoflagellate species. It is a toxic species common in warm temperate to tropical 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 1/3 to 1/2 hypotheca). The shape of the cell in lateral view is the most important criterion used for identification (Taylor et al., 1995).
D. tripos is a very distinctive species. Cells are large, anterio-posteriorly elongated and asymmetrical with two posterior hypothecal projections; a longer ventral process and a shorter dorsal one (Figs. 1-3,5). The V-shaped processes are often toothed on their posterior ends (small knob-like spines) (Fig. 1). The well developed left sucal list (LSL) widens posteriorly and is often reticulated (Figs. 1,3) (Larsen and Moestrup, 1992, Taylor et al., 1995, Steidinger and Tangen, 1996).
The thick thecal plates are heavily areolated (Fig. 1). Cell size ranges: 90-125 µm in length and 50-60 µm in dorso-ventral width (Larsen and Moestrup, 1992, Taylor et al., 1995).
Thecal Plate Description:
The small epitheca is made up of four plates. The cingulum is narrow with two well developed lists, anterior cingular list (ACL) and posterior cingular list (PCL), oriented anteriorly. The ACL is supported by many ribs (Figs. 2,5). The wide ACL forms a narrow, funnel-like structure obscuring the epitheca on the bottom. The sulcus is comprised of several irregularly shaped plates. The flagellar pore is housed in the sulcal area. The prominent and wide LSL has a straight margin and is supported by three ribs (figs. 1,5). A right sulcal list (RSL) is also present (Fig. 5) (Larsen and Moestrup, 1992, Taylor et al., 1995, Steidinger and Tangen, 1996).
The hypotheca, with four large plates, comprises the majority of the cell. It is long, narrowing into two tapered or pointed posterior projections: one short and dorsal, and one longer and ventral (Fig. 1). The dorsal projection is sometimes seen with a narrow list connecting two daughter cells during cell division (Fig. 4). The ventral margin of the hypotheca is straight or slightly undulate. The dorsal margin is concave below the cingulum and then convex continuing down to the dorsal projection (Larsen and Moestrup, 1992, Taylor et al., 1995, Steidinger and Tangen, 1996).
Morphology and Structure:
D. tripos is a photosynthetic species with chloroplasts (Fig. 3). D. diegensis, a smaller form very similar in morphology to D. tripos with a reduced hypothecal process, is suspected to be a gamete of the latter species (Moita and Sampayo, 1993).
Reproduction:
D. tripos reproduces asexually by binary fission. Moita and Sampayo (1993) speculate that sexual reproduction, with sexual dimorphism, is part of the life cycle for this species.
Species Comparison:
Dinophysis tripos can be confused with D. caudata; some cells of D. caudata, bearing a short hypothecal process, can superficially resemble D. tripos. However, D. tripos can be distinguished by the presence of two posterior projections (Larsen and Moestrup, 1992, Steidinger and Tangen, 1996).
Remarks:
Many authors consider Phalacroma to be synonymous with Dinophysis (Steidinger and Tangen, 1996).