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]