Source : Webster's Revised Unabridged Dictionary (1913)

Ianthina \I*an"thi*na\, n.; pl. L. {Ianthin[ae]}, E.
   {Ianthinas}. [NL., fr. L. ianthinus violet-blue, Gr. ?; ?
   violet + ? flower.] (Zo["o]l.)
   Any gastropod of the genus {Ianthina}, of which various
   species are found living in mid ocean; -- called also {purple
   shell}, and {violet snail}. [Written also {janthina}.]

   Note: It floats at the surface by means of a raft, which it
         constructs by forming and uniting together air bubbles
         of hardened mucus. The Tyrian purple of the ancients
         was obtained in part from mollusks of this genus.