(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 especially on spiral shells occupied by hermit crabs. See Illust. of Athecata.
Webster's Revised Unabridged Dictionary
| APA | Webster's. (2011). Hydractinian. Retrieved September 23, 2026, from http://smartdefine.org/hydractinian/definitions/2017973 |
| Chicago | Webster's. 2011. "Hydractinian" http://smartdefine.org/hydractinian/definitions/2017973 (accessed September 23, 2026). |
| Harvard | Webster's 2011, Hydractinian, Smart Define, viewed 23 September, 2026, <http://smartdefine.org/hydractinian/definitions/2017973>. |
| MLA | Webster's. "Hydractinian" 27 May 2011. Web. 23 September 2026. <http://smartdefine.org/hydractinian/definitions/2017973> |