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

in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Majidae 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 c ...

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

Caribbean Sea The Caribbean Sea ( es, Mar Caribe; french: Mer des Caraïbes; ht, Lanmè Karayib; jam, Kiaribiyan Sii; nl, Caraïbische Zee; pap, Laman Karibe) is a sea of the Atlantic Ocean in the tropics of the Western Hemisphere. It is bounded by Mexico ...

. It is sometimes kept in reef aquaria.

Description

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

carapace A carapace is a Dorsum (biology), 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 tor ...

longer than it is wide and large

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

(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 ( es, Golfo de México) is an oceanic basin, ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of ...

. 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 an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite. Nocturnal creatures generally have highly developed sens ...

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

scavenger Scavengers are animals that consume 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 herbivorous feeding b ...

but it also feeds on

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

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

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.

References

{{Taxonbar, from=Q5221500 Majoidea Crustaceans of the Atlantic Ocean Crustaceans described in 1818