What is "hydroida"

Hydroidea \Hy*droi"de*a\, n. pl. [NL. See Hydra, and -oid.] (Zo["o]l.) An extensive order of Hydrozoa or Acaleph[ae]. [Written also Hydroida.]

Note: This order includes the hydras and the free-swimming hydromedus[ae], 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.

Hydroida is an obsolete cnidarian order which united such animals as hydras, hydromedusae, and many marine attached hydroids. However, the group is paraphyletic and not composed from close relatives. But for the largest part, this group makes up what today is usually considered the subclass Leptolinae (or Hydroidolina) which also includes the colonial jellies of the Siphonophora which were not part of the Hydroida.

The "hydroid" cnidarians typically which grow up into large, elegantly branched forms. All the zooids of a colony are asexually produced from one parent zooid.

Examples of "hydroids" are:

• Craspedacusta sowerbyi, the freshwater "jellyfish"
• Hydra
• Air ferns, novelty "plants" and aquarium ornaments.
• Obelia
• Aequorea victoria of the suborder Leptomedusae, the crystal jelly- a bioluminescent jellyfish.