Semi-slug

Drawing of two views of Cryptella canariensis from the Canary Islands

Shell of Cryptella canariensis

An unidentified semi-slug from Uganda

Semi-slugs, also spelled semislugs, are land gastropods whose shells are too small for them to retract into, but not quite vestigial.^[1] 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.^[2] There exist about 1000 species of semi-slugs in comparison to about only 500 species of slugs.^[1]

Examples

Semi-slugs from the Neotropics:

• family Amphibulimidae: Amphibulima and Gaeotis^[2]
• family Xanthonychidae: Cryptostrakon, Semiconchula and Xanthonyx^[2]
• family Pleurodontidae: Coloniconcha prima^[2]
• Semi-slugs do exist but are exceptional in the Camaenidae.^[2]

References

1. Burton D. W. (1982). "How to be sluggish". Tuatara 25(2): 48-63. HTM.
2. Breure A. S. H. (2010). "The rediscovery of a semi-slug: Coloniconcha prima Pilsbry, 1933 (Gastropoda, Pleurodontidae) from Hispaniola". Basteria 74(4-6): 78-86.