The descriptive text, below the map, is from the Cornish Red Data Book (2009). The map on this web page depicts the organisms distribution and shows the records made pre-2000 and those made since.
Range & Status
On the continent, it is restricted to south-west Europe. Previously only noted as a rarity, the last confirmed record in the UK was on 4 July 1957 from the Moors River on the Hampshire/Dorset border (Moore, 1991).
The only confirmed Cornish records were from the River Tamar, just north of Gunnislake, in 1946.
Habitat & Ecology
The species favours slow flowing waters of streams, canals and rivers with tree lined
banks and muddy bottoms.
The only threat is the pollution of suitable sites from agricultural run-off or sewage influx; this was believed to be the cause of the demise of the Moors River population.
The only suitable habitat is a few kilometres of the River Tamar north of Gunnislake. Should the species be re-discovered in the area (gaps of up to 50 years between sightings are not unknown) then the site should be regarded as critically important. There have been some unconfirmed sightings in recent years which could give rise to some optimism!
I.J. Bennallick, S. Board, C.N. French, P.A. Gainey, C. Neil, R. Parslow, A. Spalding and P.E. Tompsett. eds. 2009. Red Data Book for Cornwall and the Isles of Scilly. 2nd Edition.Croceago Press.
The Cornish Red Data Book Project was led by the Cornwall and Isles of Scilly Federation for Biological Recorders (CISFBR). The full text and species accounts (minus the maps) are available on the CISFBR website.