Redefinition of the Dinoflagellate Genus Alexandrium Based on Centrodinium: Reinstatement of Gessnerium and Protogonyaulax, and Episemicolon gen. nov. (Gonyaulacales, Dinophyceae)

Table 1

Comparison of the morphological and ecological characters of the genera Gessnerium emend., Alexandrium emend., Protogonyaulax emend., Episemicolon gen. nov., and Centrodinium emend. Gómez & Artigas. Data based on Balech (1995), and this study.

	Gessnerium emend.	Alexandrium emend.	Protogonyaulax emend.	Episemicolon gen. nov.	Centrodinium emend.
Cell compression	Non or slightly compressed	Non or slightly compressed	Non or slightly compressed	Non compressed or slightly compressed	Moderate to highly lateral flattening
Horn or spines	No	No	No	No	Variable
Epitheca plate formula	Po, 3′(4′), 7′′ (6′′)	Po, 4′ (3′), 6′′ (7′′)	Po, 4′, 6′′	Po, 4′, 6′′	Po, 4′, 6′′
Shape of apical pore plate	Comma or fishhook	Comma	Comma	Oval or bullet	Horse-shoe
Anterior attachment pore (when present)	Right to Po	Right to Po	Right to Po	Dorsal to Po	Unreported
Shape of the equivalent gonyaulacoid first apical plate	Pentagonal	Rhomboidal	Rhomboidal	Rhomboidal	Rhomboidal
Pore in anterior sulcal	No	No	No	No	Yes
Precingular part in sulcal anterior	No	Sometimes	Sometimes	No	No
Left cingular part in the anterior sulcal plate	No	No	No	No	Yes
Median sulcal plates	Large	Small	Small	Small	Small
Accessory sulcal plates	Large	Small	Small	Small	Small
Lateral posterior sulcal plates	Right longer than left	Right and left of similar length	Similar or right longer than left	Right longer than left	Variable
Posterior sulcal plate	Large	Short, wider than long	Short, longer than wide	Short, longer than wide	Polygonal or triangular
Sulcal list	Moderate	Absent or inconspicuous	Moderate	Moderate or prominent	Very prominent
Posterior sulcal attachment (connecting) pore	Typically present in chain-forming species	Typically absent or inconspicuous	Present in chain-forming species	Present in chain-forming species	Present in chain-forming species
V-shaped anterior margin of the sulcal posterior plates	Prominent or not	Inconspicuous	Prominent	Prominent	No
Chain-forming	Variable	Rarely	Common	Variable	Variable
Habitat	Plankton, tropical to temperate seas	Plankton, cosmopolitan, bloom-forming in neritic waters	Plankton, cosmopolitan, bloom-forming in neritic waters	Plankton, tropical to temperate seas	Plankton, low abundance in open warm to tropical seas
Paralytic shellfish poisoning	No	Yes	Yes	No	No