Occasional Paper No. 20 AN ATLAS OF OXFORDSHIRE TERRESTRIAL MOLLUSCA S.J.GREGORY, Northmoor Trust and J.M.CAMPBELL Published by Oxfordshire Museums in co-operation with the Northmoor Trust Oxfordshire Museums are a division of the Department of Leisure and Arts Oxfordshire County Council, Oxfordshire Museums Store, Witney Road, Standlake, Oxon, OX8 7QG Tel: 01865 300639 Oxfordshire County Council Oxfordshire Museums Service November 2000 CONTENTS Page Introduction 1 Recording: Past and Present 1 Habitat Associations 2 Oxfordshire Biological Records Centre 3 Acknowledgements 3 Bibliography 4 Introduction to the maps and species accounts 4 General Maps: Main Towns and Natural Areas 5 Calcareous Rocks 5 Woodlands 6 Tetrad Coverage 6 Species Maps (listed alphabetically by Genus, including recent synonyms): Page Page Abida 15 Hygromia 48 Acanthinula 18 Lauria 16 Acicula 7 Lehmannia 36 Aegopinella 28 Limax 34 Arianta 50 Macrogastra 41 Arion 21 Malacolimax 36 Ashfordia 46 Milax 32 Azeca 10 Monacha 46 Balea 42 Nesovitrea 28 Boettgerilla 34 Oxychilus 29 Candidula 44 Oxyloma 9 Carychium 8 Perforatella 47 Cecilioides 40 Pomatias 7 Cepaea 51 Punctum 20 Cernuella 45 Pupilla 16 Clausilia 41 Pyramidula 11 Cochlicopa 10 Succinea 9 Cochlodina 40 Tandonia 33 Columella 12 Testacella 42 Deroceras 37 Trichia 48 Discus 20 Vallonia 17 Ena 19 Vertigo 13 Euconulus 39 Vitrea 27 Helicella 45 Vitrina 26 Helicigona 50 Zenobiella 47 Helix 52 Zonitoides 31 Oxfordshire Museums Service – Biological Records Centre Atlas of Terrestrial Mollusca INTRODUCTION The Mollusca are a large and diverse, group of mainly marine animals. Terrestrial snails and slugs belong to a small part of the Class Gastropoda. There is no real difference between a snail and a slug. In the latter the shell, so characteristic of snails, is merely reduced in size and usually internal. Most snails and slugs feed on lichens, algae, fungi or dead plant matter. Many will also scavenge corpses if encountered, but only a Glass Snail, Oxychilus draparnaudi, and the Shelled Slugs, Testacella spp., are active predators. These both feed primarily on earthworms. A few species, such as the Grey Field Slug, Deroceras reticulatum, and the Garden Snail, Helix aspersa, can be pests of crops and garden plants, but this is the exception. The Oxfordshire Molluscan fauna is not static. The majority of Oxfordshire’s 91 species of snail and slug live un-noticed in the countryside, many dependent on semi-natural habitats. As human activities put increasing pressure on the countryside some species have become amongst the county’s rarest inhabitants. Other species, such as the Garden Snail have been widely transported by human activities and have been spread well beyond their natural range. This process continues today and recent colonists of the county include the Greenhouse Slug, Lehmannia valentiana, which has now been found outdoors at a few garden centres. RECORDING: PAST AND PRESENT The terrestrial Mollusca are one of the most well worked invertebrate groups within Oxfordshire. The visual attractiveness and wide range of colour varieties exhibited by many species made them popular with Victorian collectors. During the 19th century numerous local lists were published, mainly for the Henley, Banbury and Oxford districts. Towards the end of the century these were collated by Collinge (1891) to give the first full county list complete with details of distribution. The 64 species included most of the county’s known rarities. In the 1920’s much work was undertaken by two emminent conchologists: the Rev. L.W.Grensted and A.E.Ellis. Four species were added to the county list: the elusive snails Vertigo substriata and V. moulinsiana and the slugs Arion intermedius and Malacolimax tenellus. Four additional species were added through taxonomic splitting of species aggregates. For example, Vallonia costata and V. excentrica were distinguished from V. pulchella. Similarly, Candidula gigaxii and Trichia plebeia were also added. This period cumulated with the publication of the Victoria County History of Oxfordshire (VCH) (Grensted 1938) with records collated for 72 species. Fieldwork undertaken by the Bureau of Animal Population Studies, based at Oxford University, generated many species records from the 1930’s onwards (the ’Wytham Survey’). Further taxonomic splits added Carychium tridentatum, Cochlicopa lubricella, and Vitrea contracta. In the 1960’s and 1970's Dr H.J.M.Bowen undertook surveys on local nature reserves. Largely neglected since the turn of the century, the early 1980’s generated many slug records, including those of M.R.Hughes. The slugs Arion fasciatus, A. silvaticus and Deroceras panormitanum (caruanae) are recorded for the first time. Since the late 1980's there has been a concerted effort by Dr A.I.Spriggs and the authors to achieve a balanced recording effort across the county within all habitats, including man-made Oxfordshire Museums Service – Biological Records Centre 1 Atlas of Terrestrial Mollusca (synanthropic) sites, such as churchyards. The presence of five additional snails, Columella aspersa, Euconulus alderi, Perforatella subrufescens, Perforatella rubiginosa and most recently, Hygromia cinctella has been confirmed in the county. Six slugs, all strongly associated with man-made habitats, have also been discovered: Arion lusitanicus, A. flagellus, A. distinctus, Tandonia budapestensis, Boettgerilla pallens and Lehmannia valentiana. To date 91 species have been recorded from Oxfordshire. To the end of October 2000, over 20,000 site-based species records are held on the Oxfordshire Biological Records Centre (OBRC) computerised database (using RECORDER). The majority of these records are post 1990. The collection of data is ongoing. HABITAT ASSOCIATIONS Snails tend to be much more numerous on lime-rich soils, due to the requirement of lime for shell building. Slugs are not so dependent on lime and sites with acidic soils can be important for slugs, despite supporting a limited snail fauna. Some species, such as Desmoulin’s Whorl Snail (Vertigo moulinsiana) or the Ash-black Slug (Limax cinereoniger), have precise habitat requirements, which makes them good indicators of undisturbed semi-natural habitats. Unfortunately this also makes such species vulnerable to habitat change and degradation. As increasing pressure is put on the countryside for farming, forestry, housing and new roads these have become some of the county’s rarest inhabitants. Deciduous woodland: This is the natural climax vegetation of southern England and has proved the most diverse of the semi-natural habitats. Within Oxfordshire, well over 40 species are regularly encountered within semi-natural ancient deciduous woodland, especially where these lie over lime-rich soils, hold plenty of dead wood and support waterlogged (flushed) areas. Six species, Acicula fusca, Vertigo substriata (wet areas), Ena montana, Limax cinereoniger, Malacolimax tenellus and Perforatella subrufescens are confined to such prime habitat. Other typical woodland inhabitants are Azeca goodalli, Cochlodina laminata, Macrogastra rolphii and to a lesser extent the slugs Limax maximus and Lehmannia marginata. Calcareous fen and riverside marsh: Wetland is another important semi-natural habitat for slugs and snails within the county, provided they are not cut for hay or too heavily grazed. About 40 species are frequently encountered. Characteristic species include Succinea putris, Oxyloma pfeifferi, Vallonia pulchella, Zonitoides nitidus, Deroceras laeve, Euconulus alderi and Ashfordia granulata. Undisturbed wetland, with intact hydrology, is important for the locally scarce Whorl Snails Vertigo antivertigo, V. substriata (if shaded), and V. moulinsiana and the nationally rare Perforatella rubiginosa. Calcareous Grassland: The lime-rich, free draining soils favour snails that are adapted to the generally dry conditions. Herb-rich short turf grassland supports a specialist snail community characterised by Pupilla muscorum and the common Vallonia excentrica. Two declining species, Abida secale and Helicella itala are confined to such habitat. Helicigona lapicida, once widespread, is now extinct at its known grassland sites. More frequent species, such as Vertigo pygmaea, Candidula intersecta and C. gigaxii, will also inhabit rougher areas. Where there is a good mosaic of grazed short turf, rough grass and scrub up to 40 species can be Oxfordshire Museums Service – Biological Records Centre 2 Atlas of Terrestrial Mollusca collected. Open scrub is important for two species, Pomatias elegans and the uncommon Roman Snail Helix pomatia. Limestone Walls: To a snail, these are nothing more than a poorly vegetated grassland and tend to support similar species. None-the-less old limestone walls, especially if mossy, hold a distinctive fauna. This is characterised by Pyramidula rupestris, Lauria cylindracea. Less frequently, the Tree Snail Balea perversa and the rarities Vertigo pusilla and Helicigona lapicida may be found. A similar species assemblage occurs on roofs tiled with ‘Cotswold slate’ limestone. Churchyards and Gardens: Man-made (synanthropic) habitats, even in urban areas, can be as diverse as many semi-natural sites. Such sites not only hold a wide range of the more generalist woodland and grassland species, but also a great variety of non-native species, accidentally introduced by human activity. Commonly encountered species include the snails Trichia striolata and Helix aspersa and the slugs Arion ater, A. distinctus, A. hortensis, Tandonia budapestensis