Hydractinian
Pronunciation : Hy`drac*tin"i*an
Part of Speech : n.
Etymology : [See Hydra, and Actinia.] (Zo?l.)
Definition : Defn: 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.
Source : Webster's Unabridged Dictionary, 1913