Laboratory culture and taxonomy ofHymenomonas coronata andOchrosphaera verrucosa (Class Prymnesiophyceae) from the Northwest Pacific

Hymenomonas coronata andOchrosphaera verrucosa, both members of the coccolithophorids, Class Prymnesiophyceae, have been studied by means of electron microscopy and with the aid of laboratory culture. Living specimens of these two species were collected in temperate and subtropical regions of Japan, including the Kii Peninsula and the Ryukyu Islands, and unialgal cultures were established in the laboratory. Their life histories are fundamentally identical, and consist of a non-motile vegetative stage that produces motile cells. The vegetative stage is either unicellular, or a packet consisting of a few cells. Both the non-motile cells and the motile cells are covered with two kinds of scales: these are thin scales of unmineralized nature and coccoliths. These two species differ from each other in the shape of the coccoliths and in the presence or absence of visible rudimentary haptonema, and they have been in separate families. The present study reveals that both species are fundamentally identical in the structure and the distribution of major organelles, especially with respect to two opposed pyrenoids which bulge from chloroplasts, each being traversed by two thylakoid bands, and a group of microtubules forming a flagellar root. On the basis of these characteristics, it would appear more logical to place these two species in the same family, namely the Hymenomonadaceae.