Dinophysis caudata

Dinophysis caudata is a producer of okadaic acid, the toxin implicated in DSP. It also produces PTX 2.

Dinophysis caudata reproduces asexually by binary fission.

D. caudata has a distinctive hypothecal protruberance. The cells are often found in pairs.

D. caudata is a distinctive species, 70-170 µm long, with a long hypothecal protruberance. The body is widest at the base of the hypothecal protruberance and narrowest near the cingulum. The anterior and posterior cingular list are very dissimilar in shape. The anterior list forms a high funnel, obscuring the epitheca. The posterior cingular list is very narrow dorsally and widens slightly ventrally. Sulcal lists: The left sulcal list extends along the length of the main body. R1 points anteriorly and R3 posteriorly. R2 is almost straight. The ribs are spaced equal distances apart.

The morphology of this species varies considerably, these differences have resulted in the description of sub-species and different forms. Since this is a worldwide distributed species, the morphological difference could be due to environmental fluctuations.

D. caudata occurs worldwide. D. caudata is common in temperate to tropical neritic waters. It occurs only occasionally around the British Isles , predominantly in spring and summer in the south west of England.

D. caudata is a cosmopolitan planktonic species (Abè 1967; Fukuyo et al. 1990; Larsen & Moestrup 1992; Taylor et al. 1995; Steidinger & Tangen 1996). Redtides associated with mass mortality of fish has been reported in the Gulf of Thailand and Seto Inland Sea in Japan (Okaichi 1967).

D. caudata is common in temperate to tropical neritic waters (Abè 1967; Fukuyo et al. 1990; Larsen & Moestrup 1992; Taylor et al. 1995; Steidinger & Tangen 1996)

Dinophysis caudata is a photosynthetic species with chloroplasts and a large posterior nucleus (Fig. 3) (Larsen & Moestrup 1992). Paired cells are common, dorsally joined at the widest point of the hypotheca (Fig. 5) (Dodge 1982; Steidinger & Tangen 1996).
D. diegensis, a species very similar in morphology to D. caudata with a reduced hypothecal process, is suspected to be a gamete of D. caudata (Moita & Sampayo 1993).

Holotype: Dinophysis caudata Saville-Kent, 1881: 455, 460
Type Locality: unknown

The morphology of this species varies considerably, in particular the length of the hypothecal projection and the dorsal expansion. These differences have resulted in descriptions of several different subspecies, varieties and forms (Dodge 1982; Larsen & Moestrup 1992; Taylor et al. 1995). Since this is a cosmopolitan species, Abè (1967) suggests the variations in morphology are due to external environmental factors (e.g. salinity, temperature and nutrients).
Many authors consider Phalacroma to be synonymous with Dinophysis (Steidinger & Tangen 1996).

D. caudata reproduces asexually by binary fission; paired cells are common (Fig. 5). Moita and Sampayo (1993) speculate that sexual reproduction, with sexual dimorphism, is part of the life cycle for this species.

Cells of D. caudata with short hypothecal processes look similar to D. diegensis (Taylor et al. 1995); D. diegensis has been called a variety of D. caudata (Steidinger & Tangen 1996). Some cells of D. caudata, bearing a short hypothecal process, can superficially resemble D. tripos (Larsen & Moestrup 1992; Steidinger & Tangen 1996).

Dinophysis caudata is an armoured, marine, planktonic dinoflagellate species. It is a bloom-forming species associated with massive fish kills. It is commonly found world-wide in subtropical and tropical neritic waters.

Dinophysis homunculus Stein, 1883

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 (Figs. 1, 2). The shape of the cell in lateral view is the most important criterion used for identification (Taylor et al. 1995).
D. caudata is a very distinctive species. Cells are large, long and irregularly subovate with a long ventral projection on the hypotheca (Figs. 1-6). The extended process varies in length and shape (Figs. 1-6), and is often toothed on its posterior end (Figs. 4,5). The long left sulcal list (LSL) extends to nearly half of the total length of the cell (Figs. 1, 2, 5, 6). This species is usually widest at the base of the LSL (Lebour 1925; Abè 1967; Dodge 1982; Fukuyo et al. 1990, Larsen & Moestrup 1992; Taylor et al. 1995; Steidinger & Tangen 1996).
The thick thecal plates are heavily areolated, each areole with a pore (Figs. 1, 4-6). Cell size ranges: 70-110 µm in length and 37-50 µm in dorso-ventral width (at base of LSL) (Lebour 1925; Abè 1967; Dodge 1982; Fukuyo et al. 1990; Larsen & Moestrup 1992; Taylor et al. 1995; Steidinger & Tangen 1996).

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), supported by ribs (Figs. 1-6). Both cingular lists are projected anteriorly (Figs. 1, 2, 5, 6). ACL forms a wide and deep funnel obscuring the epitheca (Figs. 1, 2). The sulcus is comprised of several irregularly shaped plates. The wide LSL is supported by three ribs spaced equally apart (Figs. 4-6). A right sulcal list (RSL) is also present (Figs. 1, 2, 5, 6). Both sulcal lists are often reticulated (Figs. 4,5) (Lebour 1925; Dodge 1982; Fukuyo et al. 1990; Larsen & Moestrup 1992; Taylor et al. 1995; Steidinger & Tangen 1996).
The hypotheca, with four large plates, comprises the majority of the cell. It is long and narrows ventrally into a pointed posterior projection (Figs. 1-6)(Lebour 1925). Ventral margin is generally straight or undulate along the main body (Dodge 1982; Fukuyo et al. 1990; Taylor et al. 1995; Steidinger & Tangen 1996). The dorsal contour gradually curves: it is straight or slightly concave along the anterior half of the hypotheca, then is straight or convex in the posterior half running parallel to the ventral margin. The dorsal margin may also curve sharply towards the center where it turns to continue down the ventral posterior projection, which can bear small knob-like spines (Figs. 4,5) (Lebour 1925; Dodge 1982; Fukuyo et al. 1990; Taylor et al. 1995).

Although this species is known to create red tides resulting in massive fish mortality in Japan (Okaichi 1967), the toxic potential needs to be examined further (Larsen & Moestrup 1992).