(Fabricius, 1787) 
Pachygrapsus marmoratus is a species of crab, sometimes called the marbled rock crab or marbled crab, which lives in the Black Sea, the Mediterranean Sea and parts of the Atlantic Ocean. It is dark violet brown, with yellow marbling, and with a body up to 36 millimetres (1.4 in) long. It is an omnivore, feeding on algae and various animals including mussels and limpets.
P. marmoratus has a square carapace 22–36 millimetres (0.87–1.42 in) long, which is dark violet brown with marbling in yellow. It can be distinguished from related species of Pachygrapsus in the Mediterranean Sea (Pachygrapsus maurus and Pachygrapsus transversus) by the presence of three teeth on each side of the carapace. It is capable of very rapid movements, and it uses this ability to dart into crevices, making it difficult to catch.
It is widespread in Southern Europe, from the Black Sea to the Moroccan coast, and along the Atlantic coasts of Portugal, Spain and France, and was observed as early as 1996 as far north as Southampton in the English Channel. This range expansion may be due to the warming of the surface waters.
P. marmoratus is an omnivore, but not an opportunist; crabs consume similar proportions of algae and animals however abundant they are in the crab's habitat. The favoured animals in the diet of P. marmoratus are mussels, limpets and its own species. When attacking the limpet Patella depressa, Pachygrapsus marmoratus uses a consistent method, which is usually unsuccessful. On more sheltered shores, P. grapsus eats fewer mussels, but compensates with a greater consumption of barnacles.
- Peter K. L. Ng, Danièle Guinot & Peter J. F. Davie (2008). "Systema Brachyurorum: Part I. An annotated checklist of extant Brachyuran crabs of the world" (PDF). Raffles Bulletin of Zoology 17: 1–286.
- Rose Edwards (2005). "Pachygrapsus marmoratus: a marbled rock crab". Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme. Marine Biological Association of the United Kingdom. Retrieved January 11, 2010.
- A. M. Vaccaro & C. Pipitone (2005). "First record of Pachygrapsus transversus (Gibbes, 1850) (Brachyura, Grapsidae) in Italian waters" (PDF). Crustaceana 78 (6): 677–683. doi:10.1163/156854005774353511.
- S. Cannicci, M. Gomei, B. Boddi & M. Vannini (2002). "Feeding habits and natural diet of the intertidal crab Pachygrapsus marmoratus: Opportunistic browser or selective feeder?". Estuarine, Coastal and Shelf Science 54 (6): 983–1001. doi:10.1006/ecss.2001.0869.
- Ray W. Ingle & Paul F. Clark (2006). "First reported occurrences of the marbled crab, Pachygrapsus marmoratus (Crustacea: Brachyura: Grapsoidea) in southern coastal waters of the British Isles" (PDF). JMBA2 Biodiversity Records.
- Jean-Claude Dauvin (2009). "New record of the marbled crab Pachygrapsus marmoratus (Crustacea: Brachyura: Grapsoidea) on the coast of northern Cotentin, Normandy, western English Channel". Marine Biodiversity Records 2: e92. doi:10.1017/S1755267209001109.
- Ana Silva, Diana Boaventura, Augusto Flores, Pedro Ré and Stephen J. Hawkins (2004). "Rare predation by the intertidal crab Pachygrapsus marmoratus on the limpet Patella depressa". Journal of the Marine Biological Association of the United Kingdom 84 (2): 367–370. doi:10.1017/S0025315404009294h.
- Ana Catarina Ferreira Silva, Sónia Brazão, Steve J. Hawkins, Richard C. Thompson & Diana M. Boaventura (2009). "Abundance, population structure and claw morphology of the semi-terrestrial crab Pachygrapsus marmoratus (Fabricius, 1787) on shores of differing wave exposure". Marine Biology 156 (12): 2591–2599. doi:10.1007/s00227-009-1283-1.
- Halil Şen (2007). "Food preference of Eledone moschata Lamarck, 1799 (Cephalopoda: Octopodidae) in captive conditions" (PDF). International Journal of Natural and Engineering Sciences 1 (2): 29–31.
- Inês C. Silva, Natacha Mesquita, Christoph D. Schubart, Maria Judite Alves & José Paula (2009). "Genetic patchiness of the shore crab Pachygrapsus marmoratus along the Portuguese coast". Journal of Experimental Marine Biology and Ecology 378 (1–2): 50–57. doi:10.1016/j.jembe.2009.07.032.
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