E-Flora BC: Electronic Atlas of the Flora of British Columbia

Family Description:
Members of this family of green algae also have coenocytic bodies, and, depending on the species, these can have either erect, crowded branches or be encrusting. The numerous, discoidal chloroplasts are tiny and lack pyrenoids. There is no asexual reproduction (that is, no zoospores are formed); meiosis is gametic. Gametes are formed by meiosis in gametangia on the diploid thallus; they are biflagellate and of two sizes.

Species description:
Smooth Spongy Cushion forms smooth, dark green cushions that are irregular in outline and can be 25 cm (10 in) or more in diameter and 15 mm (0.6 in) thick. These cushions occur on low intertidal rocks in very exposed locations.

In Oregon, an ascoglossan sea slug, the Branched Placida (Placida dendritica), occurs on and eats this species of Codium, with up to 32% of the Codium individuals being infested. Typically, 7 to 12 slugs are found on each occupied cushion. Apparently, the larval stages of the Branched Placida are exceedingly efficient at finding this species, as it has a refuge only where sand scour in strong wave action discourages the slugs. Many of the Codium individuals do, in fact, occur in such locations, prompting scientists to suggest that the Branched Placida might be important in determining the local distribution of this species of alga.

This species was named after William A. Setchell of the University of California, who worked on west coast algae and published from the 1890's to the 1940's.