Note:  Do not rely on this information. It is very old.


Hydroida, an order of Craspedote Hydrozoa (q.v.), including those in which the body is small, is usually fixed by an adherent base, and has a ring of tentacles around the mouth: they are rarely simple (e.g. Hydra) but are usually colonial. They are nearly all marine, but Hydra is fresh-water, and Cordylopltora (q.v.) has acclimatised itself to fresh or but slightly brackish water during the present century. The order is divided into three sub-orders: (1) the Eleutheroblastica, including the fresh-water Hydra and one or two doubtful genera; (2) the Gymnoblastica, in which the general colony (hydrosoma) is protected by a chitinous skeleton or "polypary," which does not, however, protect the polypites or individuals (Cordylopltora (q.v.) is ei very good type of this group); (3) Calyptoblastica or Thecaphora, in which the polypites are protected by expansions of the skeleton into hydrothecee or cups; these may be "sessile," being attached to the main tube as in Sertularia, or pedunculate, being borne on long stalks as in Campanularia; (4) Hydrocorallinee (q.v.), including those which form a massive calcareous skeleton.