Antaplcal horns

Fig. 10.3 Dinoflagellate cyst stage. (a) Proximate cyst of Peridinium (axial section), approx. x250. (b) Proximate cyst of fossil Gonyaulacysta, approx. x450. (c) Chorate cyst of Gonyaulax with detail of wall (axial section), approx. x250. (d) Chorate cyst of Hystrichosphaeridium, approx. x400. (e) Proximochorate cyst of fossil Spiniferites, approx. x465. (f) Proximate cyst of Deflandrea (axial section), approx. x250. (g), (h) Proximate cyst of Deflandrea: (g) ventral; (h) dorsal, approx. x360. ((b), (c), (f) Based on Sarjeant (1974); (e) based on Evitt 1969.)

its wall is an autophragm. A two-layered cyst with connections between the walls has an inner layer, the autophragm, and an ectophragm. This condition is termed holocavate. If the two layers are not connected, the cyst is known as cavate and the inner layer is called the endophragm (Fig. 10.3f-h) and the outer layer the periphragm which are partially separated, usually at the poles (Fig. 10.3f-h). The cavities thus formed (pericoels) may promote buoyancy in the cyst. Traces of the tabulation, the cingulum and the sulcus may also be seen on the periphragm, so it is probable that this type of cyst formed just below the thecal cell wall.

Parasutural

Parasutural

Penitabular

Intratabular

Penitabular

Intratabular n n t\ r\ n

Parasutural

Peritabular

Peritabular

Fig. 10.4 Surface ornament. (Redrawn after Evitt 1985.)

Parasutural septae

Gonal

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