Scavenging sand snails that surface within seconds of anything dying nearby.
Small conical to oval snails, mostly 1 to 3 cm, with a ribbed and often banded shell in cream, brown and grey, and a notch at the front of the aperture through which a long tubular siphon is extended. For most of the time the siphon is the only part on show: the animal lies buried with the tube held up out of the sand like a snorkel, drawing water over its chemical senses. Olive snails, Oliva, share the habit and the habitat but have a glossy, cylindrical, unribbed shell. Species identification needs a clean shell examined closely, and a living animal in sediment offers neither, so the genus is the sensible record.
They are scavengers with an acute sense of smell and the response is the thing worth seeing. When something dies on the sand — a fish head thrown from a boat, a crab taken and dropped — snails across a surprising radius come out of the sediment within seconds, plough across the surface with the siphon waving, and a dozen or more will be over a small carcass inside a minute or two. Between such events they work on carrion already buried in the sediment, and collectively they are a large part of what removes dead matter from a muck slope. Their egg capsules, small flat transparent envelopes stuck in rows on shell, weed and rubbish, are a common sight and are rarely recognised for what they are.
A fair proportion of the ploughing nassariids on a muck site are not snails. The shells are the right size and are abundant, so hermit crabs occupy them heavily, and the difference is in the movement: a hermit carries the shell clear of the sand and moves quickly and irregularly, while the snail drags it half-buried and leaves a furrow.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.