Hydractinian

1 definition found

From The Collaborative International Dictionary of English v.0.48 [gcide]:

  Hydractinian \Hy`drac*tin"i*an\, n. [See {Hydra}, and
     {Actinia}.] (Zool.)
     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]