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| Gessnerium emend. | Alexandrium emend. | Protogonyaulax emend. | Episemicolon gen. nov. | Centrodinium emend. |
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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 |
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