The Kerry slug or Kerry spotted slug (Geomalacus maculosus) is a species of terrestrial, pulmonate, gastropod mollusc. It is a medium-to-large sized, air-breathing land slug in the family of roundback slugs, Arionidae. Adult Kerry slugs generally measure 7–8 cm (2.8–3.1 in) in length; they are dark-grey or brown with yellowish spots. The internal anatomy of the slug has some unusual features and some characteristic differences from the genus Arion, also part of Arionidae. The Kerry slug was described in 1843—later than many other relatively large land gastropods present in Ireland and Great Britain—an indication of its restricted distribution and secretive habits. Although the distribution of this slug species includes south-western Ireland—including County Kerry—the species is more widespread in north-western Spain and central-to-northern Portugal. Given that the slug has thus far been recorded exclusively at locations in Ireland and north-western Iberia, it can be said to tentatively possess a Lusitanian distribution. The species appears to require environments that have high humidity, warm summer temperatures and acidic soils with no calcium carbonate. The slug is mostly nocturnal or crepuscular but in Ireland it is active on overcast days. It feeds on lichens, liverworts, mosses and fungi, which grow on boulders and tree trunks. The Kerry slug is protected by conservation laws in the three countries in which it occurs. It is now known to be less dependent on sensitive, wild habitats than when these laws were introduced. Attempts have been made to establish breeding populations in captivity to ensure the survival of this slug species but these have been only partly successful.
Taxonomy and etymology The Kerry slug is a gastropod, a class of molluscs that includes all snails and slugs, including terrestrial, freshwater and marine species. The Kerry slug, a member of the order Panpulmonata, is terrestrial; it breathes air with a lung. It is in the clade Stylommatophora, members of which have two sets of retractable tentacles, the upper pair of which have eyes on their tips. Its family is Arionidae, the round-backed slugs. The Kerry slug has no keel on its back, unlike the slugs in the families Limacidae and Milacidae. Many of its anatomical features are shared with species in the genus Arion, which is a more species-rich and widely distributed group of slugs within Arionidae. The Kerry slug is placed in the genus Geomalacus, which means "earth mollusc". The Kerry slug's scientific name is Geomalacus maculosus, where maculosus means "spotted" from the Latin word macula, a spot. The English-language common name is derived from County Kerry in the south-west of Ireland, where the type specimens that were used for the formal scientific description were collected. In 1842, a Dublin-based naturalist William Andrews (1802–1880) sent specimens he had found at Caragh Lake in County Kerry to the Irish biologist George James Allman. The next year, Allman exhibited them at the Dublin Natural History Society and published a formal description of the new species and genus in the London literary magazine The Athenaeum. The full scientific name, including the taxonomic authority, is Geomalacus maculosus Allman, 1843. The synonyms are other binomial names that were given over time to this taxon by authors who were unaware that the specimens they were describing belonged to a species already described by Allman. The species' binomial name is sometimes written as Geomalacus (Geomalacus) maculosus because the genus Geomalacus contains two subgenera; the nominate subgenus (subgenus of the same name) Geomalacus and a second subgenus Arrudia Pollonera, 1890. The subgenus Geomalacus contains only one species, the Kerry slug; three species comprise Arrudia. The Kerry slug has been included in molecular phylogenetics studies since 2001.
Description
The body length of adult Kerry slugs is 7–8 cm (2.8–3.1 in). These slugs are difficult to measure accurately because of their unusual startle response. Kerry slugs can also elongate themselves within crevices up to 12 cm (4.7 in). Official measurements of this species vary; Kerney et al. (1983) give a range of measurements of 6–9 cm (2.4–3.5 in). The body of a fixed (preserved) adult specimen was 7 cm (2.8 in) long with a mantle length of 3 cm (1.2 in).
The body of the Kerry slug is glossy and is covered on both sides with about 25 longitudinal rows of polygonal granulations. The slugs have two colour morphs, brown and black. In Ireland the black morph occurs in open habitats and the brown morph occurs in woodland; this correlates with the colours of the surroundings, suggesting camouflage. Experiments indicate the dark colouration is induced by exposure to light as the slug develops. There is also variation in banding; on each side of the body there can be two bands: one band just below the summit of the back and the other band further down the side of the body. When these bands are present they usually extend the whole length of the body and are overspread by numerous, ovoid yellow spots that are distributed approximately in five longitudinal zones.
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