Seaweed
"Seaweed" is a colloquial term and lacks a formal definition. A seaweed may belong to one of several groups of multicellular algae: the red algae, green algae, and brown algae. As these three groups do not have a common multicellular ancestor, the seaweed are in a polyphyletic group. In addition, some tuft-forming bluegreen algae (Cyanobacteria) are sometimes considered to be seaweed.
Seaweed blenny
The seaweed blenny is a diurnal species and feeds mostly on algae. The diet also includes such invertebrates as polychaete worms, crustaceans and hydroids, which it picks off the substrate with its beak-like mouth. A male may have several females in his territory, all of which deposit their eggs in a shared nest. This is in a crevice in a rock, inside a sponge, in a mollusc shell or in a can or other piece of discarded human debris. The male guards the nest until the eggs hatch. The larvae are planktonic at first, settling on the seabed when about long.