This snail has a fragile purple shell, which is almost completelly smooth.

They are found floating on the surface of the sea, attached to a raft of bubbles, below which it’s eggs are suspended.

Violet snails at the surface of the ocean and prey on Portuguese man-o-war (Physalia physalis) and the by the wind sailor (Velella velella).

They are all born as males and become females later in life. Shells occasionally wash ashore in huge numbers.
Often found washed up on beaches around the Bay of Plenty.

NZ Coastal Marine Invertebrates; Vol 1