Family Description:
Tetrasporangia are intercalary and tetrahedrally divided. The carpogonial branch is four cells long.

Species description:
At first glance, it is difficult to understand why Sea Belly is classified as a red alga, since it is mostly dark green to dark brown in color, but its reddish base reveals its true affinities. It has a perennial holdfast that is irregular in shape, and this gives rise to erect, annual branches up to 25 cm (10 in) tall. The branches, which are loosely forked in a somewhat dichotomous pattern, are cylindrical and up to 3 mm (about 0.1 in) in diameter. Each individual has several of these main branches; their lower parts are solid and mostly lack side branches. The upper parts of the main branches carry terminal branchlets that are up to 20 mm (0.8 in) long, hollow, constricted at the base, are blunt-tipped and have transverse diaphragms internally. These terminal branchlets are sometimes severely cropped by invertebrate herbivores and can be hard to find.

Male and female gametophytes are separate individuals. The spermatia are produced in irregular patches on the surfaces of the ultimate branchlets, while the mature cystocarps form as small pimples protruding above the surface of the branches. Sea Belly grows attached to rocks, and can also be found in tidepools.

Source:  North Pacific Seaweeds