‖ Hydrozoa, n. pl. Zool.
(haɪdrəʊˈzəʊə)
[mod.L. (Owen 1843), f. hydro- e, as combining form of hydra 6 + Gr. ζῶον animal.]
A class of Cœlenterate animals, chiefly marine, simple or more frequently compound, found in all parts of the world, and differing widely in form and complexity of structure; the individual zooid consists of a soft gelatinous sac composed of an outer and inner layer of cells (ectoderm and endoderm), and usually with tentacles surrounding the mouth. Familiar examples are the fresh-water Hydra, and the various organisms called Acalephs, Medusæ, or Jelly-fishes. Also in sing. hydrozoon (-ˈzəʊɒn), an animal of this class.
| 1843 Owen Invert. Anim. vii. 82 The first and lowest organised class [of Radiata], which I have called Hydrozoa. Ibid. Gloss., Hydrozoa, the class of Polypi organised like the Hydra. 1858 Huxley (title) Monograph of the Oceanic Hydrozoa. 1870 Nicholson Man. Zool. 67 The Hydrozoa are all aquatic, and the great majority are marine. 1877 Huxley Anat. Inv. Anim. iii. 111 The embryo sponge is..similar to the corresponding stage of a hydrozoon, and is totally unlike any known condition of a protozoon. |
Hence hydroˈzoal, hydroˈzoan, hydroˈzoic adjs., of or belonging to the class Hydrozoa. hydroˈzoan n., an animal of this class.
| 1869 Huxley Crit. & Addr. (1873) 315 The formation of a radiate Medusa upon a Hydrozoic stock. 1870 Nicholson Man. Zool. I. 96 There are no fossil remains which would be universally conceded to be of a Hydrozoal nature. 1877 Le Conte Elem. Geol. ii. (1879) 244 A compound Hydrozoan allied to Sertularia. 1880 Libr. Univ. Knowl. II. 563 The equivalent of the individual comatula is the hydrozoic stock plus all the Medusae which proceed from it. |