slug (zoology)

Soft-bodied land-living gastropod (type of mollusc) related to the snails, but without a shell, or with a much reduced shell. All slugs have a protective coat of slime and a distinctive head with protruding tentacles. The eyes are at the end of the tentacles, which are also used to smell and locate food. Slugs eat dead animal matter and plants; some species are carnivorous and eat other slugs, snails, and earthworms. Slugs are hermaphrodite (having both male and female organs). They can fertilize themselves, but usually mate with another. Slugs can live for up to three years, and are invertebrates (animals without backbones).

Behaviour
Water can quickly be lost from the slug's body, so, to prevent drying out, slugs normally come out to feed only at night or when it is wet. During dry weather they shelter in crevices, hide under rocks or go underground. The slug moves by gliding its flattened body (foot) over the ground, leaving a slimy mucus trail.

Types of slug
Land slugs belong to two groups, the roundbacks and the keeled slugs. Roundbacks, such as the slugs found in gardens, are usually about 2–3cm/0.7–1 in long and have soft fleshy sausage-shaped bodies. Keeled slugs, such as the great grey slug, are usually longer, growing up to 20 cm/6.4 in long, and they have a ridge or keel along their backs.

Classification
Slugs belong to the animal phylum Mollusca (molluscs), class Gastropoda (slugs and snails). There are over 40,000 species of gastropod and most land and freshwater slugs belong to a group called the pulmonates. The great number of land species include the common garden slug (Arion hortensis) and the great grey slug (Limax maximus).