Hydroids

Description

Hydroids can look like delicate lace, tiny branching colonies, or even floating “jelly” drifters depending on the species. Underwater, they’re frequently found attached to rocks, pilings, and seaweed, where they can form shimmering, fingerlike growths.

Orders

Anthoathecate sea anemones & relatives

Anthoathecata

Leptothecate hydroids

Leptothecata

Siphonophores (colonial jellyfish)

Siphonophorae

Thick-skinned jellyfish (Trachymedusae)

Trachymedusae

Taxonomy