Abstract: Resting cysts play an important role in the life cycle of some dinoflagellates and are considered to be one of the initiation factors of algal blooms. We desc ribed the types and morphological diversity characters of Scrippsiella trochoidea (Stein) Loeblich cysts from in situ sediment samples and in different culture conditions. S. trochoidea cells were maintained in f/2 or f/2-Nat 20°C with a 12 h light/12 h dark cycle. After 14 or 8 days incubation, respectively, the resting cysts were observed in the two different media. After 30 days, the cultures were preserved in darkness, and 4 types of resting cysts were found after another 90 days: (1) spherical to ovoid cysts (25-39 μm long) covered by asparse or numerous calcareous attachments (1-4 μm long) and a calcareous surface; (2) spherical cysts (29-35 μm diameter) with a noncalcareous surface attachment, calcareous surface; (3)spherical to ovoid cysts (29-35 μm long) w ithout any surface attachment and a calcareous surface; and (4) spherical c ysts (24- 35 μm diameter) without any surface attachment and an organic surf ace. The first type of cysts was the most common: 77.70% and 95.18%, respectively, in the two different cultures. The cysts from sediments were primarily of the first type, which have calcareous attachment, and the fouth type, with an organic wall without any attachment, was infrequent. We disc uss the reasons for the different morphology of S. trochoidea cysts produced during culture and the morphology of cysts from sediments.

Key words: morphology, resting cyst, Scrippsiella trochoidea