gonidia

Gonidia, or gonidium (plural gonidia), are specialized asexual reproductive cells found in certain colonial algae, especially among the volvocine green algae such as Volvox and Pandorina. In these organisms, the colony is typically composed of somatic cells forming the outer layer, with one or more interior cells differentiating into gonidia to serve reproductive functions. Gonidia are usually larger than somatic cells and often lack the flagella characteristic of the somatic cells.

Development and function: Gonidia arise from somatic cells through differentiation and then undergo multiple rounds of mitotic divisions to produce new offspring. In Volvox, for example, gonidia inside a parent colony reproduce to form one or more daughter colonies that mature within the parent. The daughter colonies are released when the parent disintegrates or, in some species, are budded off as separate entities, enabling rapid asexual propagation.

Lifecycle and variation: The number of gonidia per colony and their developmental timing vary by species and strain. Gonidial reproduction provides a mechanism for population growth under favorable conditions without the need for sexual fusion.

Taxonomic note: The term gonidium has historical usage in the description of various algae and related organisms. In modern literature, it is most closely associated with volvocine algae and their asexual reproductive strategy, though the concept is described in broader contexts as well. The term is generally contrasted with sexual reproduction and gamete formation.