Definition of Hydroidea
1. n. pl. An extensive order of Hydrozoa or Acalephæ.
Medical Definition of Hydroidea
1.
An extensive order of Hydrozoa or Acalephae.
Alternative forms: Hydroida.
This order includes the hydras and the free-swimming hydromedusae, together with a great variety of marine attached hydroids, many of which grow up into large, elegantly branched forms, consisting of a vast number of zooids (hydranths, gonophores, etc), united by hollow stems. All the zooids of a colony are produced from one primary zooid, by successive buddings. The Siphonophora have also been included in this order by some writers. See Gymnoblastea, Hydromedusa, Gonosome, Gonotheca.
Origin: NL. See Hydra, and -oid.
Source: Websters Dictionary
(01 Mar 1998)
Lexicographical Neighbors of Hydroidea
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