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The Acalephæ; one of the classes of coelenterates, including the Hydroidea, Discophora, and Siphonophora.

Of or pertaining to the Hydrozoa.

A comprehensive group of Invertebrata, mostly marine, comprising the Anthozoa, Hydrozoa, and Ctenophora. The name implies that the stomach and body cavities are one. The group is sometimes enlarged so as to include the sponges.

The hard parts or skeleton of various Anthozoa, and of a few Hydrozoa. Similar structures are also formed by some Bryozoa.

An extensive order of Hydrozoa or Acalephæ. [Written also Hydroida.]

One of the Hydrozoa.

The middle layer of the gonophore in the Hydrozoa.

A shoot or bud of a plant; a polyp or zooid of the compound Hydrozoa Anthozoa, etc.; also, an individual, in the narrowest sense, among the higher animals. Haeckel. True corms, composed of united personæ . . . usually arise by gemmation, . . . yet in sponges and corals occasionally by fusion of several originally disti…

Same as Hydrozoa.

An extinct division of Hydrozoa which includes the graptolities.

An order of pelagic Hydrozoa including species which form complex free-swimming communities composed of numerous zooids of various kinds, some of which act as floats or as swimming organs, others as feeding or nutritive zooids, and others as reproductive zooids. See Illust. under Physallia, and Porpita.…

A hydrozoan reproductive zooid or gonophore which does not become medusoid in form or structure. See Illust. under Athecata.