Leach's spider crab (Inachus phalangium)

Distribution data supplied by the Ocean Biodiversity Information System (OBIS). To interrogate UK data visit the NBN Atlas.Map Help



Inachus phalangium is a small spider crab with a triangular carapace up to 2 cm long and 1.7 cm across its base. It has a narrow V-shaped rostrum with an extremely narrow slit separating the rostral horns. The carapace bears three tubercles in a triangle formation on its upper surface, with the largest at the rear. It has a brownish-red carapace with slightly lighter limbs. The upper surface of the carapace and limbs are coverd in hook-like hairs. This species has very long, slender legs and sturdy claws, usually held folded under the body. These claws are particularly large in male individuals. The propodus is short and inflated, with the second limbs being thicker and longer than the others.

Recorded distribution in Britain and Ireland

This species has been recorded on all coasts of Britain and Ireland.

Global distribution



Inachus phalangium can be found on mixed coarse substrata and frequently at the base of Anemonia viridis (see additional information). It is a sublittoral species usually found between 5-11 m but can also be present down to depths of over 50 m.

Depth range


Identifying features

  • Triangular carapace up to 2 cm long and 1.7 cm across base.
  • Bownish-red carapace with lighter legs.
  • Long slender legs and sturdy chelae.
  • Slender V-shaped rostrum with a narrow slit separating the rostral horns.
  • The carapace bears three tubercules in a triangle formation.

Additional information

Inachus phalangium is often found in association with Anemonia viridis. This species is egg bearing throughout the year, producing planktivorous larvae. The carapace and limbs of this species may be concealed by encrusting epifauna, primarily sponge and algae often, renduring it difficult to see.

Inachus phalangium may be confused with either Inachus dorsettensis or Inachus leptochirus. In Inachus dorsettensis, the tubercules on the carapace are more prominent, arranged with four tubercules at the front with a fifth behind them. However these features are often concealed by epiphyte growth. Therefore the U-shapped rostrum without the slit is a more reliable distinctive feature from Inachus phalangium. Inachus leptochirus has an identicle tubercule arrangement on the carapace but differs from Inachus phalangium in its widely separated rostral horns.

Listed by

- none -


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  11. Naylor, P., 2003. Great British Marine Animals. Plymouth: Sound Diving Publications.


  1. Centre for Environmental Data and Recording, 2018. Ulster Museum Marine Surveys of Northern Ireland Coastal Waters. Occurrence dataset https://www.nmni.com/CEDaR/CEDaR-Centre-for-Environmental-Data-and-Recording.aspx accessed via NBNAtlas.org on 2018-09-25.

  2. Fenwick, 2018. Aphotomarine. Occurrence dataset http://www.aphotomarine.com/index.html Accessed via NBNAtlas.org on 2018-10-01

  3. Kent Wildlife Trust, 2018. Kent Wildlife Trust Shoresearch Intertidal Survey 2004 onwards. Occurrence dataset: https://www.kentwildlifetrust.org.uk/ accessed via NBNAtlas.org on 2018-10-01.

  4. National Trust, 2017. National Trust Species Records. Occurrence dataset: https://doi.org/10.15468/opc6g1 accessed via GBIF.org on 2018-10-01.

  5. NBN (National Biodiversity Network) Atlas. Available from: https://www.nbnatlas.org.

  6. OBIS (Ocean Biodiversity Information System),  2024. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. www.iobis.org. Accessed: 2024-07-14

  7. South East Wales Biodiversity Records Centre, 2018. SEWBReC Myriapods, Isopods, and allied species (South East Wales). Occurrence dataset: https://doi.org/10.15468/rvxsqs accessed via GBIF.org on 2018-10-02.


This review can be cited as:

Rowley, S.J. 2008. Inachus phalangium Leach's spider crab. In Tyler-Walters H. and Hiscock K. Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 14-07-2024]. Available from: https://www.marlin.ac.uk/species/detail/2198

Last Updated: 08/05/2008