IANTHINA

I*an"thi*na, n.; pl. L. Ianthinæ, E. Ianthinas. Etym: [NL., fr. L. ianthinus violet-blue, Gr. (Zoöl.)

Definition: 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.

Source: Webster’s Unabridged Dictionary 1913 Edition