Temporal range: 0.11–0Ma
|Adult O. quadrata by a burrow entrance|
(Fabricius, 1787) 
Ocypode quadrata, known as the Atlantic ghost crab, is a species of ghost crab, once described as an "occult, secretive alien from the ancient depths of the sea". It is a common species along the Atlantic coast of the United States, where it is the only species of ghost crab; its range of distribution extends from its northernmost reach on Rhode Island's beaches south along the coasts of the tropical Western Atlantic Ocean to the beach of Barra do Chui, in Rio Grande do Sul in Southern Brazil.
Adults are greyish or the colour of straw, and approximately 5 centimetres (2 in) wide at maturity. They must return to water periodically in order to moisten their gills, and when larvae must be released into the sea, but are otherwise terrestrial. Their stalked compound eyes can swivel to give them 360° vision. Young crabs are cryptically coloured to blend in with their sandy habitat.
O. quadrata is found from Block Island, Rhode Island to Santa Catarina, Brazil, on Fernando de Noronha and Bermuda. Its planktonic larvae have been found even further north, at Woods Hole, Massachusetts, although the adults cannot survive there.
O. quadrata lives in burrows in sand above the strandline. Older individuals dig their burrows further from the sea, some starting as much as 400 metres (0.25 mi) inland. Burrows can be up to 1.3 metres (4 ft 3 in) deep, and can be closed off with sand during hot periods.
O. quadrata can produce a variety of sounds, by striking the ground with the claw, by stridulation with the legs, and an incompletely explained "bubbling sound". Males compete in a heavily ritualised manner which prevents the need for physical contact.
Sandy beaches, a habitat frequented by ghost crabs, have seen a decrease in the abundance of ghost crabs due to human behavior. Ghost crabs are negatively impacted by human and vehicle trampling which results in direct crushing of crabs as well as indirect damage such as compression of sediment which reduces habitat suitability, interference with reproductive behaviors, reduction in food supply, and light pollution. Consequently O. quadrata is less common on beaches frequented by people.
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- Graziani de Freitas Antunes, Ana Paula Nunes do Amaral, Fabiana Pinto Ribarcki, Elenir de Fátima Wiilland, Denise Maria Zancan, Anapaula Sommer Vinagre (2010). "Seasonal variations in the biochemical composition and reproductive cycle of the ghost crab Ocypode quadrata (Fabricius, 1787) in Southern Brazil". Journal of Experimental Zoology 313A (5): 280–291. doi:10.1002/jez.593. PMID 20127661.
- Media related to Ocypode quadrata at Wikimedia Commons