Description: Shell tightly coiled within a moderately raised spire. Whorls fairly convex with deep sutures. The specific name indicates the very wide (hollowed out) umbilicus. Surface horn-coloured to translucent greenish, glossy with coarse growth lines. The animal is variable, from pale grey to nearly black. In acidic woods in areas of base-poor rocks. 5.3-6 mm.

World Distribution: Restricted to coastal regions on the periphery of the North Sea and to the British Isles. Distribution type: Oceanic Temperate (71).

Irish Distribution: The only obligate calcifuge ("lime-hating") land mollusc in Ireland and absent from the central plain and from eastern counties except for two very isolated colonies in Mourne Park and Rostrevor Forest, Co. Down and a few localities in the Wicklow Hills. Widespead but uncommon in the west, favouring areas of acidic bedrock.

Ecology:

• Essentially a woodland species living in acid birch or oak litter
• Adapted to base-deficient conditions including lagg woodland of raised bogs where its companions may include Discus rotundatus, Columella aspera and Oxychilus alliarius
• Strangely absent from lagg woods in eastern counties

Key Identification Features:

• Characterised by its very deep and broad umbilicus, rather like that of Discus rotundatus
• Shell a depressed cone of about 5½ whorls.
• Whorls fairly convex with deep sutures
• Surface very glossy, brown or translucent greenish
• Animal usually dark but may be pale (see first photo)

Red list status:

• Vulnerable (VU).

Distribution Map from NBN: Zonitoides excavatus at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Zonitoides excavatus at iNaturalist World Species Observations database.

GBIF data for Zonitoides excavatus | Classification: Gastropoda, Stylommatophora, Gastrodontidae, Zonitoides

Thumbnails for genus Zonitoides