A number of lineages of

crab Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all the ...

s have evolved to live predominantly on land. Examples of terrestrial crabs are found in the families

Gecarcinidae The Gecarcinidae, the land crabs, are a family of true crabs that are adapted for terrestrial existence. Similar to all other crabs, land crabs possess a series of gills. In addition, the part of the carapace covering the gills is inflated and e ...

and Gecarcinucidae, as well as in selected genera from other families, such as ''

Sesarma ''Sesarma'' is a genus of terrestrial crabs endemic to the Americas. Many species within this genus live in mangroves. They have evolved to be fully terrestrial, which means they do not have to return to the sea even to spawn. Several species i ...

'', although the term "land crab" is often used to mean solely the family Gecarcinidae.

Terrestriality and migration

No clear distinction is made between "terrestrial", "semiterrestrial", and "aquatic" crabs. Rather, a continuum of terrestriality is displayed among the true crabs, although most land-adapted crabs must still return to water to release their

eggs Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...

. Some species of terrestrial crabs can be found many kilometres from the sea, but have to complete annual migrations to the sea. For example, following the Indian Ocean

monsoon A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with annual latitudinal oscil ...

, the

Christmas Island red crab The Christmas Island red crab (''Gecarcoidea natalis'') is a species of land crab that is endemic to Christmas Island and Cocos (Keeling) Islands in the Indian Ocean. Although restricted to a relatively small area, an estimated 43.7 million a ...

(''Gecarcoidea natalis'') migrates ', forming a "living carpet" of crabs. The crabs can travel up to in a day, and up to in total. Only a few land crabs, including certain '' Geosesarma'' species, have direct development (the mother carries the eggs until they have become tiny, fully developed crabs), and these do not need access to water to breed. Many crabs belonging to the family

Potamidae Potamidae is a family of freshwater crabs. It includes more than 650 species and nearly 100 genera, which are placed into two subfamilies: Potaminae and Potamiscinae. Subfamily Potaminae The Potaminae Ortmann, 1896 are distributed around the Me ...

, which contains mostly freshwater crabs, have developed a semiterrestrial (for instance the genus ''

Nanhaipotamon ''Nanhaipotamon'' is a genus of freshwater crabs, in the subfamily Potamiscinae, found in southern China and Taiwan. As of 2018, 18 species have been described. The genus is named after the South China Sea (; literally: 'South Sea'), for it oc ...

'') to terrestrial life history, and are sometimes independent of fresh water for reproduction (for instance the genus ''

Tiwaripotamon ''Tiwaripotamon'' is a genus of freshwater crabs, recorded from China and Vietnam. Species * '' Tiwaripotamon annamense'' (Balss, 1914) * '' Tiwaripotamon araneum'' (Rathbun, 1904) * '' Tiwaripotamon austenianum'' (Wood-Mason, 1871) * '' Tiwari ...

'').

Ecology

Terrestrial crabs have often evolved from freshwater crabs, since the

physiological Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...

changes needed for living in

fresh water Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...

are

preadaptation Exaptation and the related term co-option describe a shift in the function of a trait during evolution. For example, a trait can evolve because it served one particular function, but subsequently it may come to serve another. Exaptations are common ...

s for terrestrial living. On some

oceanic island An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as water. Very small islands such as emergent land features on atolls can be called islets, skerries, cays or keys. An island ...

s, terrestrial crabs occupy the top of the

energy pyramid An ecological pyramid (also trophic pyramid, Eltonian pyramid, energy pyramid, or sometimes food pyramid) is a graphical representation designed to show the Biomass (ecology), biomass or Primary production, bioproductivity at each trophic level ...

References

External links

* {{Cite Americana, wstitle=Land Crabs , short=x Crabs Terrestrial crustaceans Arthropod common names

Terrestriality and migration

Ecology

See also

References

External links