The lavender-coloured shell of this snail is often washed up in large numbers on northern west coast beaches. Occasionally one also finds the remains of the deep purple body of the animal and of the raft of bubbles on which this unusual snail floats at the surface in tropical waters. There are three different species of this genus which are likely to be found in New Zealand waters. Another related group of planktonic snails is the group of species known as pteropods or “winged feet”. Where Janthinas are washed up, one often finds also the shells of Spirula, the ram's-horn shell, a white shell coiled in a flat open spiral. This, however, is not from a snail, but forms part of the internal skeleton of a larger mollusc related to the octupus and squid.
by Richard Morrison Cassie, M.SC.(N.Z.), D.SC.(AUCK.), Senior Lecturer in Zoology, University of Auckland.