Hydroids are small colonial animals that are often confused as plants. They grow as attached bushy growths on pilings, rocks, seaweeds and other benthic strata. The individual hydroid animals or zooids, are composed of a stem-like pedicel and a flower-like hydranth which usually contains a central mouth and tentacles. The zooids in most local species are similar in appearance but in some species the zooids differentiate into distinct types.

Gonothecae are sexual buds which can give rise to free-swimming hydromedusae (jellyfish) . These medusae are usually smaller and simpler than scyphozoans (true jellyfish)

Barnes, R.D., Invertebrate Zoology, 1980, Saunders College and Holt, Rinehart and Winston.