Calcitic resting cysts in Peridinium trochoideum (Stein) Lemmermann, an autotrophic marine dinoflagellate

Numerous calcareous cysts of the marine dinoflagellate Peridinium trochoideum (Stein) Lemmermann have been obtained from a fresh clonal culture that was isolated by incubation of a calcareous cyst from sediment in Harrington Sound, Bermuda. Electron diffraction analysis demonstrates that the crystalline spines of these cysts are composed of calcite. A few additional observations are made concerning the encystment-excystment behaviour, vegetative cell morphology, and biogeographic distribution of P. trochoideum. The phylogenetic relationships between this species and other living and fossil calcareous spore-producing dinoflagellates also are discussed briefly.