Volvox

Volvox is a green alga. It belongs to a single clade that includes colonial forms as well as the single-celled Chlamydomonas [View].

The photo (courtesy of Turtox) shows a cluster of Volvox. They average 350 µm in diameter — visible to the naked eye.

Each organism consists of over 2,000 doubly-flagellated cells (each looking like a Chlamydomonas cell) embedded in the surface of a gelatinous sphere of extracellular matrix (ECM). Within the sphere are some 16 gonidia (the darker objects).

Volvox can reproduce both asexually and sexually.

In asexual reproduction, the gonidia develop into new organisms that break out of the parent (which then dies).

• the gonidia of the males to develop into clusters of sperm and
• the gonidia of the females to develop into new spheres each of whose own gonidia develops into a pair of eggs.
• The sperm break out of the male parent and swim to the female where they fertilize her eggs.
• The zygotes form a resting stage that enables Volvox to survive harsh conditions.

The genome of Volvox carteri has been sequenced. It consists of 14,520 protein-encoding genes — only 4 more genes than in the single-celled Chlamydomonas reinhardtii!

Most of its genes are also found in Chlamydomonas. The few that are not encode the proteins needed to form the massive extracellular matrix of Volvox.