- Hydractinian
- Hydractinian Hy`drac*tin"i*an, n. [See {Hydra}, and {Actinia}.] (Zo["o]l.) Any species or marine hydroids, of the genus {Hydractinia} 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 Illust. of {Athecata}. [1913 Webster]
The Collaborative International Dictionary of English. 2000.