''Mithraculus sculptus'', the green clinging crab or emerald crab, is a species 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 ...

in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Majidae Majidae is a family (biology), family of crabs, comprising around 200 Ocean, marine species inside 52 genera, with a carapace that is longer than it is broad, and which forms a point at the front. The arthropod leg, legs can be very long in some ...

. It is a dark green colour and is found in tropical waters in the

Caribbean Sea The Caribbean Sea is a sea of the Atlantic Ocean, North Atlantic Ocean in the tropics of the Western Hemisphere, located south of the Gulf of Mexico and southwest of the Sargasso Sea. It is bounded by the Greater Antilles to the north from Cuba ...

. It is sometimes kept in reef aquaria.

Description

''Mithraculus sculptus'' is a small crab with a

carapace A carapace is a dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tortoises, the unde ...

longer than it is wide and large

chelae A chela ()also called a claw, nipper, or pinceris a pincer-shaped organ at the end of certain limbs of some arthropods. The name comes from Ancient Greek , through Neo-Latin '. The plural form is chelae. Legs bearing a chela are called chelipeds ...

(claws). The carapace is flat, shiny and green, finely sculpted, with whitish material adhering to the projections. The chelae are also green and are spoon-shaped and tipped with white. The walking legs are rather paler in colour and are hairy and often covered with encrustations. This crab grows to a length of about .

Distribution and habitat

''Mithraculus sculptus'' is native to the

and

Gulf of Mexico The Gulf of Mexico () is an oceanic basin and a marginal sea of the Atlantic Ocean, mostly surrounded by the North American continent. It is bounded on the northeast, north, and northwest by the Gulf Coast of the United States; on the southw ...

. Its range extends from the Bahamas and southern Florida to the northern part of Brazil at depths down to about . It is found in a number of varied habitats but may be most abundant in back reef environments.

Behaviour

''Mithraculus sculptus'' is largely

nocturnal Nocturnality is a ethology, behavior in some non-human animals characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnality, diurnal meaning the opposite. Nocturnal creatur ...

, hiding in caves, crevices and under rocks during the day. It is principally a

scavenger Scavengers are animals that consume Corpse decomposition, dead organisms that have died from causes other than predation or have been killed by other predators. While scavenging generally refers to carnivores feeding on carrion, it is also a he ...

but it also feeds on

algae Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...

. It is tolerant of both high and low temperatures and is capable of withstanding strong currents as it can use its legs to cling on to the

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (aquatic environment), the earthy material that exi ...

. It is often to be seen among the branches of corals such as the ''

Porites furcata ''Porites furcata'', commonly known as hump coral, thin finger coral or branched finger coral, is a species of Scleractinia, stony coral in the genus ''Porites''. It is found in the Caribbean Sea and western Atlantic Ocean. Description ''Porites ...

''. It also feeds on organisms encrusting the leaf blades of turtle grass (''Thalassia testudinum''). When threatened it often hides beneath the extended

tentacle In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work main ...

s of the sun anemone (''Stichodactyla helianthus'').

Use in aquaria

''Mithraculus sculptus'' is sometimes kept in

reef aquaria A reef aquarium or reef tank is a marine aquarium that prominently displays live corals and other marine invertebrates as well as fish that play a role in maintaining the tropical coral reef environment. A reef aquarium requires appropriately in ...

where it is said to be compatible with other reef species. It will feed on algae including bubble algae (''Valonia ventricosa'') and eat any left-over meaty foods but, if it is underfed, may consume coral polyps or small fish. Research has shown that it can be used to control excessive growth of bubble algae in aquaria, but best results are found when its diet is supplemented with

mysid Mysida is an order of small, shrimp-like crustaceans in the malacostracan superorder Peracarida. Their common name opossum shrimps stems from the presence of a brood pouch or "marsupium" in females. The fact that the larvae are reared in thi ...

s but not with pelleted food. It also possesses strong legs that can make it difficult to remove from an aquarium.

References

{{Taxonbar, from=Q5221500 Majoidea Crabs of the Atlantic Ocean Crustaceans described in 1818 Taxa named by Jean-Baptiste Lamarck