Dinophysis norvegica Claparède and Lachmann, 1858-1859
Species Overview:
Dinophysis norvegica is an armoured, marine, planktonic dinoflagellate species. This species is a bloom-forming toxic species associated with DSP events. It is commonly found in cold 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). However, size and shape varies considerably in this species (Larsen and Moestrup, 1992).
Cells of Dinophysis norvegica are generally large, ovoid and robust. The posterior end tapers to a triangular shape (Figs. 1,2). The antapex is pointed (Figs. 1,4) or slightly rounded (Fig. 3), and occasionally with small knob-like protrusions that may extend along the rounded dorsal margin (Figs. 2,5,6). This species is widest at or slightly above the middle of the cell (Fig. 7). The left sulcal list (LSL) extends about 2/3 of cell length (Balech, 1976, Dodge, 1982, Larsen and Moestrup, 1992, Taylor et al., 1995, Steidinger and Tangen, 1996).
The thick thecal plates are coarsely areolated; areolae are large and each with a pore (Figs. 1,8). Cell size ranges: 48-80 µm in length and 39-70 µm in dorso-ventral width (widest in the middle) (Balech, 1976, Dodge, 1982, Taylor et al., 1995, Steidinger and Tangen, 1996).
Thecal Plate Description:
The small epitheca is low, flat or weakly convex, and is obscured by cingular lists. It is made up of four plates with a sinuous sculpture (Balech, 1976, Dodge, 1982, Taylor et al., 1995).
The cingulum is made up of four unequal plates, all with pores. The cingulum bears two well sculptured lists: an anterior cingular list (ACL) and a posterior cingular list (PCL) (Fig. 1). In general, they are covered with irregular coarse or fine sinuous lines or reticulations (Fig. 8). Both lists are projected anteriorly (Balech, 1976, Dodge, 1982).
The sulcus is comprised of several irregularly shaped plates. The flagellar pore is housed in the sulcal area. The LSL, supported by three ribs that radiate outward, is relatively narrow (average maximum width = 10 µm) and curved to the right between the second and third rib (Fig. 1). The first and second ribs project anteriorly; the third rib is curved or straight and projects posteriorly. The third rib is located at the mid-point of the cell or just above it (Fig. 7). The sulcal lists may have conspicuous surface ornamentation, or they may be smooth (Balech, 1976, Dodge, 1982, Steidinger and Tangen, 1996).
The hypotheca, with four large plates, comprises the majority of the cell. The hypothecal outline may be smooth (Figs. 1,3,4,7), but often it is coarse with small irregular knob-like spines along the dorsal posterior end (Figs. 2,5,6). The dorsal margin is smoothly convex up to the third sulcal rib, becoming concave to straight to the antapical end, which is generally narrowly rounded or triangular shaped (Figs. 1,3,7). The ventral margin is straight or convex becoming concave at the antapex (Balech, 1976, Dodge, 1982, Larsen and Moestrup, 1992).
Morphology and Structure:
Dinophysis norvegica is a photosynthetic species with yellow chloroplasts and a posteriorly oriented nucleus (Fig. 2) (Schiller, 1933, Larsen and Moestrup, 1992).
Dimorphic cells of D. norvegica were found in Danish waters: one theca half was smaller with rounded margins and a pointed antapex (D. norvegica f. crassior); the other half was larger with a distinct concave indentation on the lower third of the ventral margin and a more rounded antapex (D. norvegica f. debilor). It is highly probable that these cells represent a stage in gametogenesis. Or they may be examples of natural variation within the species (Hansen, 1993).
Reproduction:
D. norvegica reproduces asexually by binary fission. Hansen (1993) speculates that sexual reproduction, with sexual dimorphism, is part of the life cycle for this species.
Species Comparison:
Dinophysis norvegica is very similar to D. acuta in shape, and thus can easily be misidentified. Balech (1976) found that the plate patterns of these two species are very similar, but are more variable in D. norvegica. These species can be differentiated by their size (although they overlap) and deepest position: D. acuta is larger and widest below the mid-section, whereas D. norvegica is smaller and widest in the middle region of the cell (Balech, 1976, Dodge, 1982, Dodge, 1985, Larsen and Moestrup, 1992, Taylor et al., 1995, Steidinger and Tangen, 1996).
Other differences between the two species include: D. acuta has a longer left sulcal list relative to its cell length (Balech, 1976); D. norvegica is more pointed at the antapex and lacks the hypothecal bulge evident in D. acuta (Dodge, 1985); the LSL in D. norvegica twists to the right between the second and third rib, and appears narrower than in D. acuta (Balech, 1976, Dodge, 1982).
Remarks:
D. norvegica is considerably variable in size and shape (Schiller, 1933, Balech, 1976). A number of forms and varieties have been described: D. norvegica var. debilor Paulsen and D. norvegica var. crassior Paulsen, both of which were subsequently raised to species level (Paulsen, 1949). Solum (1962) later considered them as different forms of D. norvegica.
Many authors consider Phalacroma to be synonymous with Dinophysis (Steidinger and Tangen, 1996).