In some cases the rhizoids are united together into larger strands, the rhizines.
Cernuum and other forms with superficial green prothalli is attached to the prothallus by a small foot, and develops at first as a tuberous body (the protocorm) bearing rhizoids; this forms a number of simple leaves, and upon it the apex of the shoot arises later.
A, Prothallus viewed from the lower surface; ar, archegonia; an, antheridia; rh, rhizoids (much enlarged).
As in the case of epiphytic brown seaweeds, the rhizoids of the epiphyte often penetrate the substance of the supporting alga.
These aggregations or colonies, as they are termed, may attached to muddy surfaces by rhizoids; Caulerpa, on the other, assume the form of a plate, a ring, a solid sphere, a hollow sphere, presents a remarkable instance of the way in which much the same a perforate sphere, a closed net, or a simple or branched filament.