The body under the shell

A snail is a gastropod: a mollusc with a muscular foot, a mantle, and, usually, a single shell. Land snails in the group Stylommatophora are the ones most people meet in a garden. The foot is the whole underside, a broad muscle that moves by waves of contraction. Above it sits the visceral hump, coiled into the shell, holding the gut, heart, kidney, and lung. The mantle is the soft cape that lines the shell and builds it. At the front of the mantle, on the right side of a typical right-handed snail, is a small opening, the pneumostome, which the animal opens and closes as it breathes.

The head carries two pairs of tentacles. The upper pair is longer and bears an eye at each tip. The lower pair is shorter and used for touch and smell. Both can be pulled inside out, like a sleeve, and both can regrow if they are damaged. The mouth sits underneath, armed with a radula: a ribbon of many tiny teeth that the snail draws across food like a rasp. You will not see the teeth without a lens, but you can see the result, a scraped patch on a leaf or a film of algae cleaned off a stone.

The shell is not a house the snail finds. It is part of the body, attached by the mantle and by a muscle that lets the animal pull itself inside. When the animal retreats, it is not hiding behind a door so much as shortening into its own skeleton. The soft body is mostly water. That is why a snail looks collapsed on a dry afternoon and plump after rain, and why salt on the skin is cruel: it pulls water out through the body wall. A field note can stop there. No snail needs to be tested to prove it.

Learn this layout once and the rest of the journal is easier. Foot, mantle, pneumostome, two pairs of tentacles, a shell that is living tissue’s mineral edge. Everything else, courtship, drought, the pond, the shore, is a variation on where that body can keep its water.