At least 60 species of hydroids live in the Puget Sound/Strait of Georgia region of northern Washington and southern British Columbia, and twice this number may be present along the entire west coast.  Most research is done on the conspicuous pelagic medusa phase of the life cycle, and much less on the more cryptic, bottom-inhabiting polyp stage.  Hydroids are generally classified as colonial, where a number of polyps live together and are interconnected, or solitary, where a single polyp lives on its own.  In colonial forms a tubular skeleton supports the polyps, but allows free movement of nutrient and energy materials between individuals.  In colonial forms, as well, there are varying degrees of division of feeding and reproductive function within the polyps.  In some species, such as Obelia, these different functions are carried out by different polyps in the same colony; in other species, such as Tubularia, reproductive and feeding functions are combined on a single polyp.

NOTE  derived from G. “hydra” referring to “water serpent”.  In Greek mythology, Hydra is the nine-headed serpent slain by Hercules.  The slaying was made more difficult because each time one of the Hydra’s heads was cut off, it was replaced by two others

NOTE  several introductions of hydroid species to the west coast have been recorded, including Maeotias (inexspectata) marginata, Moerisia sp.,and Blackfordia virginica from Black and Caspian Seas into estuarine areas of San Francisco Bay, California.  Interestingly, all specimens of the first species appear to be males, indicating that the population probably arose from introduction of only a single male polyp.  At least one other of the 2 remaining species, B. virginica, is represented by both sexes.  The authors comment on the potential for severe ecological disturbances that may result from the presence of these nonindigenous species.  Mills & Sommer 1995 Mar Biol 122: 279; Mills & Rees 2000 Sci Mar 64 (Suppl): 151; Rees & Gershwin 2000 Sci Mar 64 (Suppl 1): 73.  Photo courtesy the authors.  

Medusa of the hydroid
Maeotias marginata 4X

Phylum Cnidaria (lit. “nettle-bearing” G.), referring to the nematocysts possessed by all members of the phylum; includes sea anemones, cup corals, corals, sea pens, gorgonians, jellyfishes, hydroids

Class Hydrozoa  (lit. “water/serpent animal” G.), includes  small colonial polyps or free-living medusae, but also Portuguese-man-of-wars and related pelagic colonial forms

         Order Hydroida, including polyps and their medusae

Suborder Anthomedusae (lit. “flower medusa” G.: in Greek mythology, one of the three gorgons whose gaze would turn a person to stone); the medusa stage of the Anthomedusae is bell-shaped

Suborder Leptomedusae (lit. “slender medusa” G.), the medusa stage of the Leptomedusae is disc-shaped