MORPHOLOGY AND PAEDOGAMOUS SEXUAL REPRODUCTION IN CHLOROGONIUIM CAPILLATUM SP-NOV, (VOLVOCALES, CHLOROPHYTA)

Morphology and sexual reproduction in Chlorogonium capillatum Nozaki, Watanabe & Aizawa sp, nov. (Volvocales, Chlorophyta) originating from Miyatoko Mire, Japan, were studied under controlled laboratory conditi ons. Vegetative cells of this new species were fusiform with blunt ant erior and posterior ends, and they had a massive parietal chloroplast and numerous contractile vacuoles distributed throughout the protoplas t. Several to many Pyrenoids were randomly distributed in the chloropl ast, but they disappeared under the light microscope when grown photoh eterotrophically. During asexual reproduction, the first division took place transversely without a preceding rotation of the parental proto plast. In sexual reproduction, the parental protoplast divided success ively to form 32 or 64 small, biflagellate isogametes. After gametogen esis, the gametes did not escape from the parental cell (gametangial) wall, within which pairs of the adjoining gametes fused to form quadri flagellate zygotes. Such zygotes were then released from the parental cell wall and developed into hypnozygotes, which at maturity developed numerous thin spines or hairs on the zygote wall. On zygote germinati on four biflagellate germ cells were released from the zygote wall sep arately. This type of gametic union, ''paedogamy,'' has not previously been described in the green algae except for Chlorococcum echinozygot um Starr. Chlorogonium capillatum can be clearly distinguished from ot her described species of Chlorogonium by its numerous contractile vacu oles and blunt anterior and posterior ends in vegetative cells as well as by its unique sexual reproduction, in which paedogamous conjugatio n occurs, and numerous thin spines or hairs that develop on the hypnoz ygote walls.