Circular crab (Atelecyclus rotundatus)

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



Atelecyclus rotundatus has a reddish-brown carapace, light brown limbs, and black claws (chelae). This species has an almost circular carapace, up to 5 cm in diameter. The carapace bears short transverse, granular grooves on its upper surface and very hairy margins. There are 9-11 sharp teeth on the front and side margins of the carapace and 3 teeth between the eyes, central one being distinctly longer than the other two. Its chelipeds are robust and equal in size, with males having two large tubercules on the upper surface of the propodus. The legs (pereiopods) are slightly flattened with hairy margins. This species also has a long second antenna.

Recorded distribution in Britain and Ireland

This is a common species with records throughout the British Isles.

Global distribution



This species can be found from the shallow sublittoral down to >300 m depth off shore. It can be on sand or gravel substrates.

Depth range


Identifying features

  • Reddish-brown, almost circular carapace up to 5 cm in diameter.
  • Light brown limbs and black chelae.
  • Carapace and limb margins are very hairy.
  • Three teeth between the eyes, central one distinctly longer.
  • Long second antenna.

Additional information

Atelecyclus rotundatus bears eggs from February to September with planktonic larvae present from February to November. This species is eaten by Gadus morhua and Raja spp. Atelecyclus rotundatus may also be mistaken for the less common Atelecyclus undecimdentatus. But Atelecyclus undecimdendatus has a much broader carapace and coarser granulations than Atelecyclus rotundatus. The thumbnail crab, Thia scutellata is also similar, but lacks teeth on the front of its carapace.

Interestingly, Atelecyclus rotundatus buries itself by digging backwards into the substrata, and reverses its respiratory water flow through its branchial chambers to prevent suffocation (Tayor, 1984). In order to maintain sufficient respiratory currents, this species (akin to Carcinus maenas, Cancer pagurus, Crangon crangon, Bathynectes longipes, Corystes cassivelaunus for example) holds its chelipeds close to its body creating a respiratory channel with the larger second antenna. Taylor (1984) noted that when burried, its gill bailer (scaphognathite) beats in the opposite direction to normal, pumping water out at the base of the limbs instead of drawing water in.


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  1. Centre for Environmental Data and Recording, 2018. Ulster Museum Marine Surveys of Northern Ireland Coastal Waters. Occurrence dataset accessed via on 2018-09-25.

  2. Environmental Records Information Centre North East, 2018. ERIC NE Combined dataset to 2017. Occurrence dataset: accessed via on 2018-09-38

  3. Fenwick, 2018. Aphotomarine. Occurrence dataset Accessed via on 2018-10-01

  4. Kent Wildlife Trust, 2018. Kent Wildlife Trust Shoresearch Intertidal Survey 2004 onwards. Occurrence dataset: accessed via on 2018-10-01.

  5. NBN (National Biodiversity Network) Atlas. Available from:

  6. OBIS (Ocean Biodiversity Information System),  2024. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. Accessed: 2024-07-22


This review can be cited as:

Rowley, S.J. 2007. Atelecyclus rotundatus Circular 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 22-07-2024]. Available from:

Last Updated: 03/07/2007