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.