Helix (gastropod)

Helix is a genus of large, air-breathing land snails native to the western Palaearctic and characterized by a globular shell.

It is the type genus of the family Helicidae, and one of the animal genera described by Carl Linnaeus at the dawn of the zoological nomenclature.

Members of the genus first appeared in the fossil record during the Miocene.

Well-known species include Helix pomatia (Roman snail, Burgundy snail, or edible snail) and Helix lucorum (Turkish snail). Cornu aspersum (garden snail), though externally similar and long classified as a member of Helix (as "Helix aspersa"), is not closely related to Helix and belongs to a different tribe of Helicinae.

In Linnaeus' 10th edition of Systema Naturae, which marks the beginning of the zoological nomenclature, the generic name Helix had been used for a variety of terrestrial (e.g. Zonites algirus), freshwater (e.g. Lymnaea stagnalis), and marine (e.g. Fossarus ambiguus) gastropods. Later authors restricted the name's use to stylommatophoran species with flattened to globular shells, including zonitids and other groups. In the course of the 1800s, several thousand species of Europe and abroad have been described in Helix. By the early 1900s, the genus was split into many separate genera, leaving only species closely related to its type species Helix pomatia in the genus. However, due to the previously broad concept of the genus, Helix is part of the original combination (basionym) of many gastropod names and there still are many nominal taxa described in Helix whose generic placement remains unresolved (taxa inquirenda), although they clearly do not refer to any species of Helix in its present sense.

Since the 2000s, Helix has been subject to extensive molecular phylogenetic studies and taxonomic revisions. These led to the exclusion of several species, most notably the garden snail, and inclusion of others (H. ceratina, H. nicaeensis). Maltzanella, for long considered a subgenus of Helix, was also formally removed from the genus, but is the sister group of Helix.

Two subgenera are currently recognized:

Helix comprises large land snails species, with shell diameter of 2–6 cm. The shell is globular to conical, with five darker bands that may be variably reduced or fuse together. The globular shell distinguishes Helix from most of the related genera (tribe Helicini), except for Maltzanella and Lindholmia. The surface has a structure of fine transversal ribs, developed to a varying degree, and there may be very fine spiral grooves as well. The shell is never malleated. Colour of the foot varies. It may be grey, brown, black or pink; the back of the foot is dark in several species.