Several recent studies on the ascidian species: a brief review

Abstract

Three topics were referred to here. Firstly, the comparative studies were briefly reviewed between Ciona intestinalis (Linné) and C, savignyi Herdman, sometimes living together, inclusive of the observation that in Japan intestinalis spawns in the evening while savignyi at dawn. Secondly, the individuals of Halocynthia roretzi (Drasche) inhabiting Mutsu Bay are dividable into three types, sometimes found sympatrically, by the difference in the season and time of spawning. The season may shift, but the time seems stable, so the reproductive isolation may be suggested between these types. For several reasons, however, their occurrence was here regarded as the polymorphism or representing an early stage of sympatric speciation. Lastly, the intimate observations of the cultured colonies apparently of Botrylloides violaceus Oka revealed that they should be classified into 5 species, basing mainly on the differences in the sexual reproduction. Seemingly, further comparative studies will judge the validity of their present taxonomic rank.