Hydroids and polyzoans are often gathered and preserved as seaweeds.
Spider-crabs (Maa), for example, have their carapaces covered with alg and hydroids of all sorts.
Hydroids are colonies of associated animals living a communal life.
Found at extreme low-water mark on hydroids, shells, stones, and Fucus.
Found creeping like a small dodder-plant over other polyzoans, hydroids, ...