A number of lineages of

crab Crabs are decapod crustaceans of the infraorder Brachyura (meaning "short tailed" in Greek language, Greek), which typically have a very short projecting tail-like abdomen#Arthropoda, abdomen, usually hidden entirely under the Thorax (arthropo ...

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

Gecarcinucidae The Gecarcinucidae are a family of true freshwater crabs. They are found throughout South Asia, Southeast Asia and New Guinea, with a single genus found in Australia. Taxonomy The family Parathelphusidae is now demoted to the rank of subfamily ...

, as well as in selected genera from other families, such as '' Sesarma'', 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. 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 The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or approximately 20% of the water area of Earth#Surface, Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia (continent), ...

monsoon A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in Atmosphere of Earth, atmospheric circulation and precipitation associated with annu ...

, the Christmas Island red crab (''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, which contains mostly freshwater crabs, have developed a semiterrestrial (for instance the genus '' Nanhaipotamon'') to terrestrial life history, and are sometimes independent of fresh water for reproduction (for instance the genus '' Tiwaripotamon'').

Ecology

Terrestrial crabs are often similar to

freshwater crab Around 1,300 species of freshwater crabs are distributed throughout the tropics and subtropics, divided among eight family (biology), families. They show direct development and maternal care of a small number of offspring, in contrast to marine c ...

s, since the

physiological Physiology (; ) is the science, scientific study of function (biology), functions and mechanism (biology), mechanisms in a life, living system. As a branches of science, subdiscipline of biology, physiology focuses on how organisms, organ syst ...

changes needed for living in

fresh water Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salt (chemistry), salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include ...

are preadaptations for terrestrial living. On some

oceanic islands An island or isle is a piece of land, distinct from a continent, completely surrounded by water. There are continental islands, which were formed by being split from a continent by plate tectonics, and oceanic islands, which have never been ...

, terrestrial crabs occupy the top of the energy pyramid.

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