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Prorocentrum minimum (Pavillard) Schiller, 1933

Species Overview:

Prorocentrum minimum is an armoured, marine, planktonic, bloom-forming dinoflagellate. It is a toxic cosmopolitan species common in cold temperate brackish waters to tropical regions.

Taxonomic Description:

Prorocentrum minimum is a bivalvate species often observed in valve view. Cells are small (14-22 µm long to 10-15 µm wide) and shape is variable: cells range from oval (Figs. 1,4-6,8,9), to triangular (Fig. 7) or heart-shaped (Fig. 10). Cells are laterally flattened (Fig. 2). A short apical spine is sometimes observable (Figs. 1,4,6,8-10). Valves with short, evenly shaped broad-based spines (about 600-700 per valve) arranged in a regular pattern (Figs. 1,2). These can appear as rounded papillae depending on angle of view. There are two sized pores present: smaller pores are scattered (Fig. 1), while larger pores are located at the base of some peripheral spines (Figs. 8,10). The pores appear hooded. The intercalary band is transversely striated (Figs. 2,6,7,9) (Parke and Ballantine, 1957, Faust, 1974, Dodge, 1982, Steidinger and Tangen, 1996).

The broad anterior end is truncate with a relatively small, shallow, broadly V-shaped depressed periflagellar area located apically on the right valve slightly off-center (Figs. 1-4). The periflagellar area bears eight apical platelets and two pores of unequal size: a large flagellar pore and a smaller auxiliary pore (Fig. 3). Adjacent to the flagellar pore is a small apical spine. Adjacent to the auxiliary pore is a small curved forked periflagellar collar (Fig. 3) (Parke and Ballantine, 1957, Dodge and Bibby, 1973, Faust, 1974).

Morphology and Structure:

Prorocentrum minimum is a photosynthetic species with golden-brown chloroplasts, one large pyrenoid and two pusules (Figs. 4,5). The nucleus is broadly ellipsoidal and posteriorly situated (Parke and Ballantine, 1957, Faust, 1974, Dodge, 1982).

Reproduction:

P. minimum reproduces asexually by binary fission.

Species Comparisons:

P. minimum can be confused with P. balticum; however, the former species differs by its larger size and different shape, and by having only one apical spine and a forked periflagellar collar (Faust et al., 1999).

Ecology:

P. minimum is a bloom-forming planktonic species. Cosmopolitan in cold temperate brackish waters to tropical regions; mostly estuarine, but also neritic (Steidinger and Tangen, 1996, Faust et al., 1999). Due to its small size, this species is probably often lost or overlooked in field samples (Dodge, 1982). Cells are active swimmers (Parke and Ballantine, 1957).

Recently, Stoecker et al., 1997 reported mixotrophy in this species; ingested cryptophytes were observed in cells of P. minimum.

Toxicity:

P. minimum is a toxic species; it produces venerupin (hepatotoxin) which has caused shellfish poisoning resulting in gastrointestinal illnesses in humans and a number of deaths. This species is also responsible for shellfish kills in Japan and the Gulf of Mexico, Florida (Nakazima, 1965, Nakazima, 1968, Okaichi and Imatomi, 1979, Tangen, 1983, Shimizu, 1987, Smith, 1975, Steidinger and Tangen, 1996).

Habitat and Locality:

P. minimum is commonly found along the west coast of the USA, Japan, Gulf of Mexico, Caspian, Adriatic, Mediterranean and Black Seas, and Scandinavian waters; often in large numbers (Dodge, 1982, Tangen, 1980, Tangen, 1983, Marasovic et al., 1990).

Prorocentrum minimum