Pisania striata is a marine snail in the Buccinidae family. It is a common species in the Mediterranean Sea. It is a scavenger or predator, but I found no detailed information about its food. Its habitat include rocky seashore (eulittoral zone or intertidal zone) and in the sublittoral zone not far from the shore (subtidal zone).
The height of the shell is up to 30 mm. There are fine spiral striae on its shell sculpture. The specific name striata is derived from those striate.
This one is from the Dubrovnik-Neretva County, southern Croatia. I have taken this photo in situ in very shallow water (about 2-3 cm) with an ordinary non-water-proof camera. Maybe it can be a motivation for anybody to take photos of marine animals with any camera. You just need to take care about reflections from the water level.
Its body is black. It extend its siphon through the siphonal notch during crawling, because there are chemoreceptors in the siphon and the snail is searching for its prey:
Dance S. P. (ed.) (1974). The Encyclopedia of Shells. Blanford Press, ISBN 0713706988, page 145.