Morphology and sexual reproduction of Gonium multicoccum (Volvocales, Chlorophyta) from Nepal

* Dedicated to Professor Mitsuo Chihara (University of Tsukuba, Japan) on the occasion of his official retirement.

Abstract

Strains of Gonium (Volvocales, Chlorophyta) were isolated from a soil sample collected in Nepal. They generally produced 16- or 32-celled colonies with multipyrenoid cells, but 8-celled colonies were occasionally observed. Vegetative morphology observed by light and electron microscopy and embryogenesis indicated that this entity is referable to G. multicoccum Pocock, but differs in some respects from the original description of G. multicoccum. In addition, sexual reproduction in these Nepalese strains was unusual with regard to gametic union and zygote germination. Isogametes lacked tubular mating structures (mating papillae), which are seen in the anterior region of the gametes in other Gonium species as well as in other isogamous genera of the volvocacean and astrephomenacean algae. Plasmogamy was initiated by direct attachment between the surfaces of the two gametic protoplasts. The attaching sites were apparently randomly located on the gametic protoplasts. The germinating zygote usually gave rise to four separate biflagellate gone cells, rather than a colony of four.