Coleochaetales: More on Morphology

Coleochaete pulvinata

The "chaete" in the names of the genera refer to long, sheathed hair cells which cover the algal surface. These are believed to defend the alga against potential herbivores. Flagella are present on both sperm cells and zoospores; two are inserted on each of these cell types, and are arranged asymmetrically over a multilayered structure (MLS).

Members of the Coleochaetales have a variety of morphological forms. Species of both genera may grow as branched filaments, while other species may be pseudoparenchymatous. Two species of Coleochaete are parenchymatous and disc-shaped; these also have complex gametangia.

One of these two species, Coleochaete orbicularis, also has cells associated with the embedded zygote which resemble the placental transfer cells in plants. The surfaces of these cells have complicated membrane ingrowths which increase their total membrane surface area, and may facilitate transfer of nutrients to the zygote.

Source:
Handbook of Protoctista, ed. by L. Margulis, 1990 Jones and Bartlett, chapter 32d by Linda Graham.

Photo of Coleochaete pulvinata reproductive series courtesy Charles Delwiche.