1. 
   Hydractinian
   Hy`drac·tin'i·an noun [ See Hydra , and Actinia .] (Zoology) 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 stone...
   Found op http://www.encyclo.co.uk/webster/H/74
   
   
2. 
   hydractinian
   <zoology> 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 especially. On spiral shells occupied by hermit crabs. ... See: Hydra, and Actinia. ... Source: Websters Dictionar...
   Found op http://www.mondofacto.com/facts/dictionary?hydractinian
   
   
3. 
   Hydractinian
   • (n.) 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.
   Found op http://thinkexist.com/dictionary/meaning/hydractinian/
   
   

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