|1.||of or relating to the Hydroida, an order of colonial hydrozoan coelenterates that have the polyp phase dominant|
|2.||(of coelenterate colonies or individuals) having or consisting of hydra-like polyps|
|3.||a hydroid colony or individual|
|[C19: from |
|hydroid (hī'droid') Pronunciation Key
Any of numerous, usually colonial marine coelenterates of the order Hydroida, having a polyp rather than a medusoid form as the dominant stage of the life cycle. Hydroids have a simple cylindrical body with a mouthlike opening surrounded by tentacles. Most species form colonies with individual hydroids branching off from a common hollow tube that is probably used to share ingested food. The young develop from eggs or from buds. The most well-known hydroids are the hydras (genus Hydra), which are atypical in being both freshwater and solitary.