PLEUROCHRYSIS-PLACOLITHOIDES SP-NOV (PRYMNESIOPHYCEAE), A NEW MARINE COCCOLITHOPHORID WITH REMARKS ON THE STATUS OF CRICOLITH-BEARING SPECIES

The main characteristics of the unique cricoliths of Pleurochrysis placolithoides sp. nov., a marine coccolithophorid isolated from the coast of Belle-Ile-en-Mer (France), are considerable development of the distal ring and heterogeneity in size. Their convex shape and overlapping elements further distinguish the coccoliths which superficially resemble placoliths. Ultrastructural features are similar to those of other members of the genus, including details of the flagellar apparatus and coccolithogenesis, and a heteromorphic life cycle is demonstrated in culture. Cricolith-bearing organisms are discussed and it is concluded that two distinct groups of species may be distinguished based on differences in coccolith morphology. Following this study P. placolithoides is shown to be related to Cricosphaera gayraliae. The family Pleurochrysidaceae fam. nov. is established for coccolithophorids with authentic cricoliths and a new combination is also proposed: P. roscoffensis (Dangeard) comb. nov. © 1991 Taylor & Francis Group, LLC.