information on the biology of species and the ecology of habitats found around the coasts and seas of the British Isles

Scorpion spider crab (Inachus dorsettensis)

Distribution data supplied by the Ocean Biogeographic Information System (OBIS). To interrogate UK data visit the NBN Atlas.
Only coastal and marine records shown



Inachus dorsettensis has a triangular shaped shell (carapace) with long slender legs and a U-shaped snout-like projection (rostrum). It has four small spines on the anterior part of carapace upper surface. The carapace is reddish brown in colour. The underside of the claw bearing limb (cheliped) is bright pink or violet in colour especially the segment behind the claw (the carpus). Female chelipeds are small and the claw (propodus) is somewhat compressed. Male chelipeds are large, with a short and swollen propodus. The carapace length is around 3.5 cm, with a breadth of 2.7 cm. The eye stalks are also totally visible from above.

Recorded distribution in Britain and Ireland

Widely distributed around the British Isles with sparse records along the east coast of England and west coast of Ireland.

Global distribution

Recorded in the north east Atlantic from mid Norway southwards to the Spanish Sahara (West Africa), probably the whole of the Mediterranean.


Inachus dorsettensis occurs in coastal waters from about 4 m to at least 300 m offshore on various substrates such as sand, muddy sand and seaweed-covered rocky beds.

Depth range


Identifying features

  • Chelipeds equal in size.
  • Carapace triangular, and longer than broad.
  • U-shaped cleft separating each half of the rostrum.
  • Well developed spines ranging across the anterior part of the carapace.

Additional information

Inachus dorsettensis covers itself in tiny pieces of sponge and sea weed to provide camouflage. It is often found living in the tentacles of the snakelocks anemone (see Ingle, 1996 for further details).

Listed by

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Further information sources

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  1. Bradshaw, C., Veale, L.O., Hill, A.S. & Brand, A.R., 2002. The role of scallop-dredge disturbance in long-term changes in Irish Sea benthic communities: a re-analysis of an historical dataset. Journal of Sea Research, 47, 161-184.

  2. Bryant, A.D. & Hartnoll, R.G., 1995. Reproductive investment in two spider crabs with different strategies. Journal of Experimental Marine Biology and Ecology, 188, 261-275.

  3. Crothers, J. & Crothers, M., 1988. A key to the crabs and crab-like animals of British inshore waters. Somerset, England: Field Studies Council. [AIDGAP guide, no. 155.]

  4. Fish, J.D. & Fish, S., 1996. A student's guide to the seashore. Cambridge: Cambridge University Press.

  5. Hall-Spencer, J.M., Froglia, C., Atkinson, R.J.A & Moore, P.G., 1999. The impact of Rapido trawling for scallops, Pecten jacobaeus (L.), on the benthos of the Gulf of Venice. ICES Journal of Marine Science, 56, 111-124

  6. Hartnoll, R.G., Bryant, A.D. & Gould, P., 1993. Size distribution in spider crab populations - spatial and temporal variation. Journal of Crustacean Biology, 13, 647-655.

  7. Hayward, P.J. & Ryland, J.S. (ed.) 1995b. Handbook of the marine fauna of North-West Europe. Oxford: Oxford University Press.

  8. Howson, C.M. & Picton, B.E., 1997. The species directory of the marine fauna and flora of the British Isles and surrounding seas. Belfast: Ulster Museum. [Ulster Museum publication, no. 276.]

  9. Ingle, R., 1997. Crayfishes, lobsters and crabs of Europe. An illustrated guide to common and traded species. London: Chapman and Hall.

  10. Ingle, R.W., 1980. British Crabs. Oxford: British Museum (Natural History), Oxford University Press.

  11. Ingle, R.W., 1996. Shallow-water Crabs, (2nd edn). Shrewsbury: Field Studies Council. [Synopses of the British Fauna, no 25]

  12. JNCC (Joint Nature Conservation Committee), 1999. Marine Environment Resource Mapping And Information Database (MERMAID): Marine Nature Conservation Review Survey Database. [on-line]

  13. Lebour, M.V., 1927. Studies of the Plymouth Brachyura. I. The rearing of crabs in captivity with a description of the larval stages of Inachus dorsettensis, Macropodia longirostris and Maia squinado. Journal of the Marine Biological Association of the United Kingdom, 14, 795-821.

  14. National Biodiversity Network (NBN) Atlas website. Available from:  Accessed 01 April 2017


This review can be cited as:

Edwards, R.V. 2005. Inachus dorsettensis Scorpion spider crab. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 19-09-2018]. Available from:

Last Updated: 01/11/2005