tentacle sheath

from The Collaborative International Dictionary of English v.0.48

Tentacle \Ten"ta*cle\, n. [NL. tentaculum, from L. tentare to
   handle, feel: cf. F. tentacule. See {Tempt}.] (Zool.)
   A more or less elongated process or organ, simple or
   branched, proceeding from the head or cephalic region of
   invertebrate animals, being either an organ of sense,
   prehension, or motion.
   [1913 Webster]

   {Tentacle sheath} (Zool.), a sheathlike structure around the
      base of the tentacles of many mollusks.
      [1913 Webster]