''Libinia emarginata'', the portly spider crab, common spider crab or nine-spined spider crab, is a species of

stenohaline Stenohaline describes an organism, usually fish, that cannot tolerate a wide fluctuation in the salinity of water. Stenohaline is derived from the words: "''steno''" meaning narrow, and "''haline''" meaning salt. Many fresh water fish, such as g ...

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 ...

that lives on the Atlantic coast of

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

Distribution

''Libinia emarginata'' occurs from Nova Scotia to the

Florida Keys The Florida Keys are a coral cay archipelago located off the southern coast of Florida, forming the southernmost part of the continental United States. They begin at the southeastern coast of the Florida peninsula, about south of Miami, and e ...

and through the Gulf of Mexico. It lives at depths of up to , with exceptional records of up to .

Description

''Libinia emarginata'' is roughly triangular in outline and very heavily calcified, 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 ...

about long and a leg span of . The whole crab is khaki, and the carapace is covered in spines and tubercles, and, as with other

decorator crabs Decorator crabs are crabs of several different species, belonging to the superfamily Majoidea (not all of which are decorators), that use materials from their environment to hide from, or ward off, predators. They decorate themselves by sticking ...

, often clothes itself in debris and small invertebrates.

Reproduction

Mating takes place, and eggs are produced from June to September. The eggs are initially a bright orange-red, but turn brown during development, which takes around 25 days. The eggs then hatch as zoea larvae, and the female can produce another brood of eggs within 12 hours, unlike many other crab species whose females only mate immediately after

molting In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is the manner in which an animal routinely casts off a part of its body (often, but not always, an outer ...

Similar species

''Libinia emarginata'' is very similar to '' Libinia dubia'' with which it is largely

sympatric In biology, two related species or populations are considered sympatric when they exist in the same geographic area and thus frequently encounter one another. An initially interbreeding population that splits into two or more distinct species sh ...

. They can be told apart by examining the row of spines along the center of the carapace: in ''L. emarginata'' there are nine, while in ''L. dubia'' there are only six. Also, the rostrum of ''L. dubia'' is more deeply forked than that of ''L. emarginata''.

Ecology and behavior

''Libinia emarginata'' lives on various substrates, at depths of up to . Adults are sluggish and not aggressive, and younger crabs are frequently covered with sponges and hydroids. Despite its small size, in comparison to other predatory crabs, ''L. emarginata'' feeds on large

starfish Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea (). Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or basket stars. Starfish ...

such as '' Asterias forbesi''. Unusually for crabs, ''L. emarginata'' preferentially walks forwards, rather than sideways, although they are also capable of sidelong movement. Its skeletal, muscular and neural anatomy more closely resembles that of forward-walking species, rather than that of more closely related sideways-walking species. ''L. emarginata'' will mate in large aggregations. These aggregations may function as a protective mechanism during reproduction. Males of ''L. emarginata'' show an unusual "

obstetrical Obstetrics is the field of study concentrated on pregnancy, childbirth and the postpartum period. As a medical specialty, obstetrics is combined with gynecology under the discipline known as obstetrics and gynecology (OB/GYN), which is a surgic ...

behavior", in which gravid females who are about to release their larvae are held behind the male and aggressively protected.

References

{{Taxonbar, from=Q5234006 Majoidea Crustaceans of the Atlantic Ocean Crustaceans described in 1815 Taxa named by William Elford Leach