Assessment Rationale:

This species was proposed as Endangered B2ab(iii) by Seddon (2008) as it is found in two areas on one offshore islet, which are both very small, and where habitat decline is possible. Following evaluation, this was reclassified as Critically Endangered (CR) B1ab(iii)+2ab(iii) as populations have been reduced to the single islet off Porto Santo and the species is vulnerable to possible impact of introduced small rodents and competition from Theba pisana. The species is the only representative of the genus Idiomela. It is currently listed on the Annex II of EU Habitats and Species Directive and on the list of protected species for the Bern Convention, rodent control needs review to determine the impact on this species on the islet. The revision of the listing as Vulnerable in 1996 is based on the increased perception of threat to larger gastropod species, which are not as abundant as smaller helicids, and are easier to find, and hence are more vulnerable to predation.

Geographic Range:

This species is endemic to the Madeiran islands, originally found on the island Porto Santo during the Quaternary (Cameron et al. 2006), but it is now only known living on at two sites on the small islet of Ilheu de Baixo off the southwest coast of Porto Santo (Seddon 2008; Groh and Cameron, pers. comm., 2010).

Population:

The population trend is unknown, but this species is more vulnerable to predation by rodents than other smaller crag and scree species on the island.

Habitat and Ecology

This large ground-dwelling helicid is found in grassland and rocky slopes on the islet.

Major Threat(s):

The species are vulnerable to predation by rodents, as the species is a large gastropod which would be predated. Other possible risks to the species would include competition from Theba pisana and possibility of fire, although as the island is a protected area, there is less likelihood of fire as there is no tourist access to the islands.

Conservation Actions

This species is currently listed on the Annex II of EU Habitats and Species Directive and on the list of protected species for the Bern Convention, the regional government has designated a protected area for the species. However, rodent control needs review to determine the impact on this species, amongst others on the islet.