A HETEROMORPHIC LIFE-CYCLE IN 2 COASTAL COCCOLITHOPHORIDS, HYMENOMONAS-LACUNA AND HYMENOMONAS-CORONATA (PRYMNESIOPHYCEAE)

Species of the genus Hymenomonas, with the exception of the freshwater species Hymenomonas roseola, are marine littoral coccolitfiophorids, characterized by coccoliths of the tremalith type. A heteromorphic lif e cycle involving an alternation between coccolith-bearing cells and s cale-bearing cells has been established for Hymenomonas lacuna in cult ure. The scaly cells are covered by two types of scales, morphological ly distinct from those of the coccolith-bearing stage. Both scale- and coccolith-bearing stages may be motile or nonmotile. The number of ch romosomes in coccolith-bearing cells is, however, about twice that in scaly cells as indicated by nuclear staining. Both life-cycle generati ons were also observed in Hymenomonas coronata, and this type of heter omorphic life cycle could be general for all heterococcolithophorids w ith tremaliths.