Prorocentrum gracile Schütt, 1895
Species Overview:
Prorocentrum gracile is an armoured, marine, planktonic, bloom-forming dinoflagellate. This cosmopolitan species is found in cold temperate and tropical waters.
Taxonomic Description:
P. gracile is a bivalvate species often observed in valve view. Cells are small to medium-sized (45-55 µm in length and 25-30 µm in width) and elongate to lanceolate; they are more than twice as long as broad (Figs. 1,3,4). The anterior part of the cell is broad and rounded with a strong winged apical spine; the posterior end tapers to a point (Figs. 1,3,4). The valve surface is covered with many shallow poroids (Fig. 1) and large radially arranged trichocyst pores (Fig. 4) (Dodge, 1975, Toriumi, 1980, Steidinger and Tangen, 1996).
The periflagellar area is a relatively small, shallow depression situated apically on the right valve off-center (Figs. 1,2). The prominent winged apical spine lies adjacent to the periflagellar area. It is long, narrow and large (Fig. 1). Directly opposite, on the other side of the periflagellar area, lies a much smaller, slightly curved apical spine (Fig. 2) (Dodge, 1975, Toriumi, 1980).
Morphology and Structure:
P. gracile is a photosynthetic species with a kidney-shaped nucleus situated posteriorly (Toriumi, 1980).
Reproduction:
P. gracile reproduces asexually by binary fission.
Species Comparison:
P. gracile is often misidentified as P. rostratum or P. micans, species similar in general shape and surface architecture. P. rostratum, however, does not have an anterior spine, but rather a rostrum that is part of the valve. P. rostratum is slender and elongate, and five or six times as long as broad. P. gracile has a much longer and stronger winged apical spine than P. micans, and is at least twice as long as broad. P. micans is tear-drop shaped and less than twice as long as broad (Wood, 1954, Dodge, 1975, Steidinger and Tangen, 1996).
P. gracile and P. micans share two distinct features: a.) similar trichocyst pore pattern (Steidinger and Williams, 1970, Steidinger and Tangen, 1996); and b.) similar arrangement of apical spines: they lie adjacent to the periflagellar area (Toriumi, 1980).