Semi-slug



Semi-slugs, also spelled semislugs, are land gastropods whose shells are too small for them to retract into, but not quite vestigial. The shell of some semi-slugs may not be easily visible on casual inspection, because the shell may be covered over with the mantle.

This is a type of gastropod that is intermediate between a slug (without an external shell) and a land snail (with a large enough shell to retract completely into).

There exist a number of gastropod families that have semi-slugs species. There exist about 1,000 species of semi-slugs in comparison to about only 500 species of slugs.

Examples
Semi-slugs have a worldwide distribution and have evolved in several families; genera include:
 * Palearctic and Nearctic
 * family Parmacellidae: Cryptella
 * family Vitrinidae: Eucobresia, Semilimax, Vitrina, Vitrinobrachium
 * Asia - Pacific
 * family Ariophantidae: Parmarion, Ratnadvipia, Varadia
 * family Helicarionidae: Attenborougharion, Helicarion, Howearion, Ibycus, Parmellops, Ubiquitarion
 * Semi-slugs also exist but are exceptional in the Camaenidae.
 * Neotropics
 * family Amphibulimidae: Amphibulima, Gaeotis
 * family Xanthonychidae: Cryptostrakon, Semiconchula, Xanthonyx
 * family Pleurodontidae: Coloniconcha prima
 * Tropical Africa
 * family Urocyclidae: Gymnarion