Synonyms: Gonyaulax tamarensis Lebour 1925; Gonyaulax tamarensis var. excavata Braarud 1945; Gonyaulax excavata (Braarud) Balech 1971; Gessnerium tamarensis Lebour) Loeblich III and L. Loeblich 1979; Protogonyaulax tamarensis (Lebour) F. J. R. Taylor 1979; and A. excavatum (Braarud) Balech and Tangen 1985.
Small to medium cells with size and shape variability. Most typically, epitheca is broadly conical with slight shoulders. The hypotheca is somewhat trapezoidal and posteriorly concave. Often the left side is longer than the right and the hypothecal profile is skewed. The Po has a strongly developed callus and the 1' has a small ventral pore. The sp is short and not attenuated. Toxic and nontoxic strains.
Remarks: This specis may still have homonyms that sort out morphologically, biochemically, or geographically with new studies.
Distribution: Coastal; western Europe from Norway to the Iberian peninsula including the British Isles, the Atlantic Ocean of the United States from Maine to 40°N, Argentina, Japan, Korea, Gulf of Thailand, Canadian Pacific, Venezuela, Barents Sea, Kamchatka peninsula in Russia, and south of Taiwain.