''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 th ...

that lives on the

Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

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 th ...

Distribution

''Libinia emarginata'' occurs from

Nova Scotia Nova Scotia ( ; ; ) is one of the thirteen provinces and territories of Canada. It is one of the three Maritime provinces and one of the four Atlantic provinces. Nova Scotia is Latin for "New Scotland". Most of the population are native Eng ...

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 The Gulf of Mexico ( es, Golfo de México) is an 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 the United ...

. 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 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 ...

about long and a leg span of . The whole crab is

khaki The color khaki (, ) is a light shade of tan with a slight yellowish tinge. Khaki has been used by many armies around the world for uniforms and equipment, particularly in arid or desert regions, where it provides camouflage relative to sandy ...

, and the carapace is covered in spines and

tubercle In anatomy, a tubercle (literally 'small tuber', Latin for 'lump') is any round nodule, small eminence, or warty outgrowth found on external or internal organs of a plant or an animal. In plants A tubercle is generally a wart-like projection ...

s, 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 ''Libinia dubia'', the longnose spider crab, is a species of crab in the family Epialtidae. It is found in shallow waters on the eastern coast of North America. Description The carapace of the longnose spider crab is nearly circular in outline. ...

'' 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 s ...

. 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 Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ships * Ros ...

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 Aggression is overt or covert, often harmful, social interaction with the intention of inflicting damage or other harm upon another individual; although it can be channeled into creative and practical outlets for some. It may occur either reacti ...

, and younger crabs are frequently covered with

sponge Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate throu ...

s and

hydroids Hydroids are a life stage for most animals of the class Hydrozoa, small predators related to jellyfish. Some hydroids such as the freshwater '' Hydra'' are solitary, with the polyp attached directly to the substrate. When these produce buds ...

. 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 a ...

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