from The Century Dictionary.
- A class of Cœlenterata, one of two prime divisions of that subkingdom, Actinozoa being the other.
from the GNU version of the Collaborative International Dictionary of English.
- noun plural (Zoöl.) The Acalephæ; one of the classes of cœlenterates, including the Hydroidea, Discophora, and Siphonophora.
from Wiktionary, Creative Commons Attribution/Share-Alike License.
- proper noun A taxonomic
classwithin the phylum Cnidaria— the hydrozoas.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- noun coelenterates typically having alternation of generations; hydroid phase is usually colonial giving rise to the medusoid phase by budding: hydras and jellyfishes
from Wiktionary, Creative Commons Attribution/Share-Alike License
Hydrozoa over Corals; Crustacea over Insecta, and Amphipoda and
The terms ectoderm and entoderm were introduced by Allman  in 1853 for the two cell-layers in the Hydrozoa.
These will contain all his important contributions to science, with the exception of a large separate treatise on the _Oceanic Hydrozoa_ published by the Ray
I am glad your journey has yielded so good a scientific harvest, and especially that you found my "Oceanic Hydrozoa" of some use.
Returning to the purpose of our interview, the researches Mr. Huxley laid before me were chiefly those on the Salpae, a much misunderstood group of marine Hydrozoa.
The most important of the unfinished work consists of the long-delayed "Oceanic Hydrozoa," the "Manual of Comparative Anatomy," and a report on Fisheries.
The Hydrozoa were represented not only by jellyfish but also by the GRAPTOLITE, which takes its name from a fancied resemblance of some of its forms to a quill pen.
I hope, supply me with figures and descriptions of the British Polyzoa and Hydrozoa, and I have confidence in my friend, Mr. Dyster of Tenby
But now that he had left the service, this objection was removed, and in June 1854 the sum of 300 pounds sterling was assigned for this purpose, while the remainder of the expense was borne by the Ray Society, which undertook the publication under the title of "Oceanic Hydrozoa."
But, though with much difficulty the scientific authorities enabled him to secure the promised Government grant for his book, and a temporary billet ashore while he worked at it, he was only able to publish his _Oceanic Hydrozoa_; a vast quantity of his researches remained unpublished, and subsequent investigators, going over the same ground, won the credit for them.