Fig. 1.

Schematic representation of the phylogenetic relationships of the volvocine algae and the parallel evolution of the spheroidal colony. Volvocine algae range from the unicellular Chlamydomonas to the multicellular Volvox through various intermediate forms and are used as a model for research into the evolution of multicellularity [3]. The spheroidal colony is thought to have evolved twice independently within this group [4, 5, 11]: once in the Volvocaceae, from Pandorina to Volvox, and the other in the genus Astrephomene. The phylogeny is based on previous reports [4–6]. All drawings and photographs represent side views of individuals with anterior ends orienting toward the top of this figure. All photographs are original