ianthina

CIDE DICTIONARY

ianthina, n. [NL., fr. L. ianthinus violet-blue, Gr. ; violet + flower.].

 Any gastropod of the genus Ianthina, of which various species are found living in mid ocean; -- called also purple shell, and violet snail.  [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]