Dinophysis caudata Saville-Kent, 1881
Species Overview:
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.
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).
D. caudata is a very distinctive species. Cells are large, long and irregularly subovate with a long ventral projection on the hypotheca (Figs. 1,2). The extended process varies in length and shape (Figs. 1,2,5), and is often toothed on its posterior end (Fig. 2). The long left sulcal list (LSL) extends to nearly half of the total length of the cell (Fig. 2). This species is usually widest at the base of the LSL (Lebour, 1925, Abè, 1967, Dodge, 1982, Fukuyo et al., 1990, Larsen and Moestrup, 1992, Taylor et al., 1995, Steidinger and Tangen, 1996).
The thick thecal plates are heavily areolated, each areole with a pore (Figs. 3,4). 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 and Moestrup, 1992, Taylor et al., 1995, Steidinger and Tangen, 1996).
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), supported by ribs (Figs. 1,3,4). Both cingular lists are projected anteriorly (Fig. 3). The wide ACL forms a wide and deep funnel obscuring the epitheca (Fig. 1). The sulcus is comprised of several irregularly shaped plates. The flagellar pore is housed in the sulcal area. The wide LSL is supported by three ribs spaced equally apart (Fig. 2). A right sulcal list (RSL) is also present (Figs. 1,4). Both sulcal lists are often reticulated (Figs. 4,5) (Lebour, 1925, Dodge, 1982, Fukuyo et al., 1990, 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 ventrally into a pointed posterior projection (Figs. 1-5) (Lebour, 1925). The ventral margin is generally straight or undulate along the main body (Dodge, 1982, Fukuyo et al., 1990, Taylor et al., 1995, Steidinger and 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 (Fig. 2) (Lebour, 1925, Dodge, 1982, Fukuyo et al., 1990, Taylor et al., 1995).
Morphology and Structure:
Dinophysis caudata is a photosynthetic species with chloroplasts and a large posterior nucleus (Fig. 2) (Larsen and Moestrup, 1992). Paired cells are common, dorsally joined at the widest point of the hypotheca (Fig. 5) (Dodge, 1982, Steidinger and 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 and Sampayo, 1993).
Reproduction:
D. caudata reproduces asexually by binary fission. Moita and de M. Sampayo (1993) speculate that sexual reproduction, with sexual dimorphism, is part of the life cycle for this species.
Species Comparison:
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 and Tangen, 1996). Some cells of D. caudata, bearing a short hypothecal process, can superficially resemble D. tripos (Larsen and Moestrup, 1992, Steidinger and Tangen, 1996).
Remarks:
The morphology of this species varies considerably, in particular the length of the hypothecal projection and the of dorsal expansion. These differences have resulted in descriptions of several different subspecies, varieties and forms (Dodge, 1982, Larsen and 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 and Tangen, 1996).