noun 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.
HYDRACTINIAN
Meaning of HYDRACTINIAN in English
Webster English vocab. Английский словарь Webster. 2012