Semislugs

Semislugs are terrestrial gastropods that lie between snails and true slugs. They possess a greatly reduced external shell, or sometimes a shell that is internal or only weakly visible under the mantle, giving them a slug-like appearance while retaining some snail features.

The shell, when present, is usually small and nonfunctional for protection. The mantle may cover much of the body, and the presence of a residual shell surface or internalized shell distinguishes semislugs from fully shelled snails and from true slugs.

Semislugs occur in warm habitats worldwide but show greatest diversity in tropical and subtropical regions, especially Southeast Asia and parts of Africa and the Pacific. They inhabit leaf litter, rotting logs, and moist soil, feeding on decaying vegetation, fungi, and microbial communities.

Most semislugs are hermaphroditic and reproduce by mating with exchange of sperm; some lay shelled eggs, others produce gelatinous egg masses. They are mainly active at night or in damp conditions to minimize water loss.

Taxonomically, semislugs are not a single natural group but an informal term for several independent lineages within terrestrial pulmonate gastropods that have reduced or internal shells. Consequently, classification varies by author, and field identifications often rely on shell remnants, soft anatomy, and geographical context.