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Rediscovery and a redescription of Vermetum festinans from La Palma, Canary Islands (Gastropoda Pulmonata: Gastrodontidae)
Abstract
Vermetum festinans was hitherto known only from a few shells collected on La Palma. It is the type species of Vermetum, which has sometimes been classified in the Pristilomatidae. The recent allocation of a second species newly discovered on Gran Canana, V. tamadabaensis, to the same genus zvas based only on close similarity of its shells to those of V. festinans. The genus zvas transferred to the Gastrodontidae from the Pristilomatidae on the basis of characters of the genital anatomy shown by V. tamadabaensis. Efforts to refind living V. festinans were successful in 2015, allowing the redescription here of its shells and habitat and the first studies of its genital anatomy. It closely resembles V. tamadabaensis anatomically, sharing the presence of a sarcobelum and three "bridges" joining parts of the distal genitalia, differing only in details. The new data therefore confirm that the genus Vermetum should be transferred to the Gastrodontidae and that two species should be recognised.
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The genital anatomy is described for all five island populations of Retinella (Lyrodiscus) endemic in the Canary Islands, revealing that it is mainly similar to that of the only species studied previously (R. circumsessa). Their shell characters, detailed distribution and habitat preferences are also described and reassessed. Five species are recognised. The population of El Hierro has hitherto been assigned to R. lenis, the species on La Palma, but it is named as a new species here. Descriptions of species from the south- west Alps by Giusti et al. (1986) revealed additional combinations of anatomical and shell characters that made it impossible to identify the limits of subgenera among the European Retinella species. Lyrodiscus was regarded by them as a possible exception to this because of its peculiar shell sculpture. Since our data show that the endemic Canary Islands species assigned to Lyrodiscus from conchological characters are also very similar to each other anatomically, it is useful to retain them together in the same subgeneric group until a phylogenetic study provides an adequate basis for a revised classification. Two additional Lyrodiscus species showing the characteristic shell sculpture are known from fossils in NW. Europe. Hence, it is argued that the species still living in the Canary Islands can most easily be regarded as relicts of a fauna that was widespread in NW. Europe in the Neogene and early Pleistocene. There, they apparently became extinct during the cold conditions of the Late Pleistocene glacial stages, whereas they survived in the milder climates within forest and scrub- covered habitats on the Canary Islands.
A new, small (<6 mm), endemic land snail species discovered recently on La Palma (Canary Islands) is described and named as Janulus traviesus. The generic placement of this new species is based on the close similarity of its shell shape and size to those of the other Macaronesian Janulus species.
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