Ianthinae

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}.] [1913 Webster]

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. [1913 Webster]