Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting tail-like abdomen, usually hidden entirely under the thorax. They live in all the world's oceans, in freshwater, and on land. They are generally covered with a thick exoskeleton. They generally have five pairs of legs, and they have pincer claws on the ends of the frontmost pair. They first appeared during the Jurassic period, around 200 million years ago.
The fiddler crab or calling crab can be one of the hundred species of semiterrestrial marine crabs in the family Ocypodidae. These crabs are well known for their extreme sexual dimorphism, where the male crabs have a major claw significantly larger than their minor claw, whilst females claws are both the same size. The name fiddler crab comes from the appearance of their small and large claw together, looking similar to a fiddle.
Ocypode is a genus of ghost crabs found in the sandy shores of tropical and subtropical regions throughout the world. They have a box-like body, thick and elongated eyestalks, and one claw is larger than the other in both males and females. They inhabit deep burrows in the intertidal zone. They are primarily nocturnal, and are generalist scavengers and predators of small animals. The genus contains 21 species.
Carcinus maenas is a common littoral crab. It is known by different names around the world. In the British Isles, it is generally referred to as the shore crab, or green shore crab. In North America and South Africa, it bears the name European green crab.
Hymenosomatidae is a family of crabs with some 110 described species in 24 genera. The following genera are placed in the Hymenosomatidae:
Majidae is a family of crabs, comprising around 200 marine species inside 52 genera, with a carapace that is longer than it is broad, and which forms a point at the front. The legs can be very long in some species, leading to the name "spider crab". The exoskeleton is covered with bristles to which the crab attaches algae and other items to act as camouflage.
Macrophthalmus is a genus of crabs which are widespread across the Indo-Pacific. It contains the following species : Species in this genus are often referred to as sentinel crabs.
Perisesarma is a genus of mangrove crabs in the family Sesarmidae predominantly found in the Indo-Pacific. Some 23 species are described as of late 2006, with two from West Africa: P. kammermani(De Man, 1883) and P. albertiRathbun, 1921. They are typically small, semiterrestrial crabs found on the forest floor at low tide. They eat nearly anything they can, and try to eat anything that does not threaten them — including pencils and other objects dropped on the forest floor. The last species of the genus described is P. samawatiGillikin and Schubart (2004). It can be found in East Africa along with P. guttatum, but its sister species is P. eumolpe from Malaysian mangroves.
Calappidae is a family of crabs containing 16 genera, of which 7 are only known as fossils:
Ranina ranina, also known as the Huỳnh Đế crab, (red) frog crab or spanner crab, is a species of crab found throughout tropical and subtropical habitats. It is often fished for its meat.
Carpilius convexus, commonly known as the marbled stone crab, is a species of crab found in the Indo-Pacific, from Hawaii to the Red Sea and South Africa. It was first described by Peter Forsskål in 1775 as "Cancer convexus", and has sometimes been treated as a variety of the larger species Carpilius maculatus. The biology of the genus Carpilius is poorly known. The coloration of Carpilius convexus is a yellow-brown or red, with patches that are mainly brown, growing up to 25 cm. Despite us knowing their size, coloration, and habitat, little else is known about their biology.
Achaeopsis spinulosa, the hotlips spider crab, is a species of crab in the family Inachidae, found only around the South African coast. It is the only species in the genus Achaeopsis.
Around 1,300 species of freshwater crabs are distributed throughout the tropics and subtropics, divided among eight families. They show direct development and maternal care of a small number of offspring, in contrast to marine crabs, which release thousands of planktonic larvae. This limits the dispersal abilities of freshwater crabs, so they tend to be endemic to small areas. As a result, a large proportion are threatened with extinction.
Calappa japonica, also known as the Japanese shame-faced crab, is a marine species of box crab in the family Calappidae. Originally found in the waters around Japan, more recently it has been found in Africa, the Red Sea and Western Australia.
Paraleptuca chlorophthalmus, is a common fiddler crab found in the mangroves of East Africa, from Somalia to South Africa, as well as Madagascar and Mauritius. Marsh fiddlers dig burrows in the muddy or sandy banks of salt marshes, which they use to protect themselves from predators, high tide and extreme temperatures. They feed by filtering detritus out of mud, and defend their burrows against other fiddler crabs. Paraleptuca chlorophthalmus is characterised by its red pereiopods and blue and black markings on its carapace.
Ocypode cursor, the tufted ghost crab, is a species of ghost crab found on sandy beaches along the coasts of the eastern Atlantic Ocean and eastern Mediterranean Sea.
Elamena is a genus of crab, containing the following species:
Hirsutodynomene is a genus of crabs in the family Dynomenidae. All species in this genus except the newest one belonged to the genus Dynomene. These two genera form the subfamilia Dynomeninae. The type species of this genus is: Dynomene spinosaRathbun, 1911.
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, for it occurs mostly in coastal areas. The genus was first described by R. Bott in 1968 as Isolapotamon (Nanhaipotamon), i.e., a subgenus of Isolapotamon.
