Libinia emarginata, theportly spider crab,common spider crab ornine-spined spider crab, is a species ofstenohalinecrab that lives on theAtlantic coast ofNorth America.

Libinia emarginata
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Malacostraca
Order:	Decapoda
Suborder:	Pleocyemata
Infraorder:	Brachyura
Family:	Epialtidae
Genus:	Libinia
Species:	L. emarginata
Binomial name
Libinia emarginata Leach, 1815 [1]
Synonyms [2]
Libinia canaliculataSay, 1817

Libinia emarginata occurs fromNova Scotia to theFlorida Keys and through theGulf of Mexico.^[3] It lives at depths of up to 160 ft (49 m), with exceptional records of up to 400 ft (120 m).^[4]

Libinia emarginata is roughly triangular in outline and very heavily calcified, with acarapace about 4 in (100 mm) long and a leg span of 12 inches (300 mm).^[4] The whole crab iskhaki, and the carapace is covered in spines andtubercles,^[5] and, as with otherdecorator crabs, often clothes itself in debris and small invertebrates.^[4]

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 aszoea larvae, and the female can produce another brood of eggs within 12 hours, unlike many other crab species whose females only mate immediately aftermolting.^[6]

Libinia emarginata is very similar toLibinia dubia with which it is largelysympatric. They can be told apart by examining the row of spines along the center of the carapace: inL. emarginata there are nine, while inL. dubia there are only six.^[5] Also, therostrum ofL. dubia is more deeply forked than that ofL. emarginata.^[4]

Libinia emarginata lives on varioussubstrates, at depths of up to 150 ft (46 m). Adults are sluggish and notaggressive, and younger crabs are frequently covered withsponges andhydroids.^[5]

Despite its small size, in comparison to other predatory crabs,L. emarginata feeds on largestarfish such asAsterias forbesi.^[7]

Unusually for crabs,L. emarginata preferentially walks forwards, rather than sideways, although they are also capable of sidelong movement.^[8] Its skeletal,^[9] muscular^[8] and neural anatomy^[10] 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.^[11] These aggregations may function as a protective mechanism during reproduction.^[11] Males ofL. 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.^[6]