Bougainvillia muscus is a marine invertebrate, a species of hydroid in the suborder Anthomedusae.

Strethill Wright reared some medusae to maturity and decided that the species was in fact Bougainvillia britannica.

However, confusion remained because the three hydroid forms, B. ramosa, B. fruticosa and B. muscus were so similar.

[2] B. muscus is a colonial hydroid forming irregular, straggling branched bushes.

When these mature, sexual reproduction occurs, the fertilised eggs settle out and new hydroids are formed.

The stomach and marginal bulbs are pink or yellowish-brown while the ocelli are black or dark red.