MolluscIreland - land and freshwater
  • Planorbarius corneus (Linnaeus 1758) Great ramshorn
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Planorbarius corneus
© Dr Roy Anderson
Planorbarius corneus
© Dr Roy Anderson

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A very large coiled shell with a typical ‘ramshorn’ shape. Flattened on the underside but spire recessed on the upper side. No trace of a keel. Glossy brownish on the upper side, lighter, more olive-brown, on the underside, but often covered with dark brown, matt deposits. Hairy when young. Introduced in many areas but widespread.

Key characteristics

  • A very large, dark, coiled shell
  • Flattened on the underside but spire recessed on the upper side
  • Whorls completely rounded with deep sutures
  • Glossy brownish on the upper side, lighter, more olive-brown, on the underside, though often covered with dark brown, matt deposits
  • Mouth wide and almost circular
  • Growth lines coarse and irregular

Size

20-35 mm.

World Distribution

Occurs from Spain northwards to southern Scandinavia and eastwards to central Siberia. Distribution type: Eurosiberian Wide-temperate (64).

Irish Distribution

Probably an early introduction to Ireland but now widespread in central Ireland where its range follows the nineteenth century canal system with one or two outliers in southern counties. In Northern Ireland it was known only from ornamental ponds e.g. at Cushendun, Antrim and Mount Stewart, Down until Welch (1933) found the species in Lough Neagh. Kerney (1968) noted it in the disused Blackwater Canal near Caledon, Armagh and in the Coalisland Canal in Tyrone, both linked to L. Neagh by the Blackwater River. Anderson (1977) found it commonly in marshes and the margins of peat bogs all round the periphery of the Lough. It was also introduced to the Quoile River System in mid Down and spread to the lake system around Ballynahinch. It has recently spread strongly through the Shannon System and has probably entered the Erne Basin through the inter-connecting Ballyconnell Canal. It is now abundant in Upper Lough Erne but has not yet reached Lower Lough Erne (March 2009).

Ecology

  • Primarily a species of lakes and large, slow-flowing rivers
  • It can survive in remarkably acidic conditions in wetlands and peaty drains - colonies of decorticate shells exist in peaty drains in the Montiaghs peatlands, Co. Antrim and along the margins of raised bog at Killycolpy, Co. Tyrone, to the east and west of Lough Neagh

Red List status

  • Least concern (lc).

Wikipedia link

Wikipedia page for Planorbarius corneus

 Anderson, R., (2016). Planorbarius corneus (Linnaeus 1758). [In] MolluscIreland.
http://www.habitas.org.uk/molluscireland/species.asp?ID=140 Accessed on 2017-10-19.