Source : Webster's Revised Unabridged Dictionary (1913)

Serpula \Ser"pu*la\, n.; pl. {Serpul[ae]}, E. {Serpulas}. [L., a
   little snake. See {Serpent}.] (Zo["o]l.)
   Any one of numerous species of tubicolous annelids of the
   genus {Serpula} and allied genera of the family
   {Serpulid[ae]}. They secrete a calcareous tube, which is
   usually irregularly contorted, but is sometimes spirally
   coiled. The worm has a wreath of plumelike and often
   bright-colored gills around its head, and usually an
   operculum to close the aperture of its tube when it retracts.