Synonym :
Prorocentrum gracile Schutt 1895

Morphological Characteristics :
Elongated cell, sometimes in "S" shape. Apical spine sharp and tiny; protruded from the anterior side. Two flagella at the anterior end. With thick and hard plates. Nucleus in "U" shape, normally at the posterior side.

Size of Specimen :
60-85 mm (L), 20-30 mm (W)
Apical spine: 9.9-16 mm (L)

Distribution :
Widely distributed in tropical and subtropical waters. Caused algae blooms at sheltered waters. Being a severe red tide causative species in Tolo Harbour, Hong Kong and Dapeng Bay, China.

Major Limiting Factors :
Inorganic nitrates and nitrites; optimal growth at N:P atomic ratios of 4-15. Favoured by low salinity (<27%o) and warm water temperature (23-28°C). Positively correlated with manganese (Mn) ions.

Toxicity :
Non-toxic; harmful to marine organisms due to oxygen depletion at high cell concentration.