GNU Collaborative International Dictionary of English

Found one definition

1.       
   ‖Ianthina , n.; pl. L. Ianthinæ , E. Ianthinas . [NL., fr. L. ianthinus violet-blue, Gr. ;  violet +  flower.] (Zool.) 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
   ☞ 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