Masses of hydroids adorn many of the offshore wrecks, mixed in with anemones, sponges, mussels, coral, and algae. Hydroids are the most primitive Cnidarians, closely related to Hydromedusae, and display the most even split between the sessile polyp stages and free-swimming medusa stages, which are quite small and common.
The common Pink-Hearted Hydroid Tubularia spp generally grows in rounded tufts up to 6" across. Siphonophores are free-living hydroids that are often highly venomous, although most attached forms are harmless to humans.
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