English dictionary
hydractinian
Definitions, examples, synonyms and antonyms from WordNet 3.0.
noun
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Any species or marine hydroids, of the genus <i>Hydractinia</i> and allied genera. These hydroids form, by their rootstalks, a firm, chitinous coating on shells and stones, and esp. on spiral shells occupied by hermit crabs. See <i>Illust.</i> of <u>Athecata</u>.
Source: webster1913