''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 (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 ...

that lives on the

Atlantic The Atlantic Ocean is the second largest of the world's five oceanic divisions, with an area of about . It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for se ...

coast of

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

Distribution

''Libinia emarginata'' occurs from

Nova Scotia Nova Scotia is a Provinces and territories of Canada, province of Canada, located on its east coast. It is one of the three Maritime Canada, Maritime provinces and Population of Canada by province and territory, most populous province in Atlan ...

to the

Florida Keys The Florida Keys are a coral island, coral cay archipelago 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 a ...

and through the

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 ...

. 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 (color), 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 rela ...

, 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 projectio ...

s, and, as with other decorator crabs, 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.

Similar species

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

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

. 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 ** podium * 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 ...

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

sponge Sponges or sea sponges are primarily marine invertebrates of the animal phylum Porifera (; meaning 'pore bearer'), a basal clade and a sister taxon of the diploblasts. They are sessile filter feeders that are bound to the seabed, and a ...

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 polygon, star-shaped echinoderms belonging to the class (biology), class Asteroidea (). Common usage frequently finds these names being also applied to brittle star, ophiuroids, which are correctly referred to ...

such as ''

Asterias forbesi ''Asterias forbesi'', commonly known as Forbes sea star, is a species of starfish in the family Asteriidae. It is found in shallow waters in the northwest Atlantic Ocean and the Caribbean Sea. Description left, Underside of ''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 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 Crabs of the Atlantic Ocean Crustaceans described in 1815 Taxa named by William Elford Leach