Libinia emarginata

Libinia emarginata occurs from Nova Scotia to the Florida Keys and through the Gulf of Mexico.{{cite book |chapter=Libinia emarginata Leach, 1815. Portly Spider Crab |title=A Picture Guide to Shelf Invertebrates from the Northern Gulf of Mexico |author=Harriet Perry |author2=Kirsten Larsen |name-list-style=amp |year=2004 |chapter-url=http://www.gsmfc.org/seamap/picture_guide/Crabs/libinia%20emarginata.pdf |publisher=Gulf States Marine Fisheries Commission |access-date=2010-04-14 |archive-date=2009-09-12 |archive-url=https://web.archive.org/web/20090912091716/http://www.gsmfc.org/seamap/picture_guide/Crabs/libinia%20emarginata.pdf |url-status=dead }} It lives at depths of up to {{convert|160|ft|abbr=on}}, with exceptional records of up to {{convert|400|ft|abbr=on}}.

Libinia emarginata is roughly triangular in outline and very heavily calcified, with a carapace about {{convert|4|in|abbr=on}} long and a leg span of {{convert|12|in}}. The whole crab is khaki, and the carapace is covered in spines and tubercles,{{cite book |title=Life in the Chesapeake Bay |author=Alice Jane Lippson |author2=Robert L. Lippson |name-list-style=amp |edition=3rd |publisher=JHU Press |year=2006 |isbn=978-0-8018-8337-8 |chapter=Crustaceans of the shallows |pages=[https://archive.org/details/lifeinchesapeake00lipp_0/page/153 153–158] |chapter-url-access=registration |chapter-url=https://archive.org/details/lifeinchesapeake00lipp_0 |url=https://archive.org/details/lifeinchesapeake00lipp_0/page/153 }} and, as with other decorator crabs, often clothes itself in debris and small invertebrates.

File:Libinia emarginata.jpg

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.{{cite journal |author=Gertrude W. Hinsch |year=1968 |title=Reproductive behavior in the spider crab, Libinia emarginata (L.) |journal=The Biological Bulletin |volume=135 |issue=2 |pages=273–278 |url=http://www.biolbull.org/cgi/content/abstract/135/2/273 |doi=10.2307/1539781|jstor=1539781 |pmid=28368760 }}

Libinia emarginata is very similar to Libinia dubia with which it is largely sympatric. 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.{{cite book |title=Marine Life of the North Atlantic: Canada to New England |author=Andrew J. Martinez |author2=Candace Storm Martinez |name-list-style=amp |publisher=Aqua Quest Publications |year=2003 |isbn=978-1-881652-32-8 |chapter=Arthropods |pages=144–175}}

Libinia emarginata lives on various substrates, at depths of up to {{convert|150|ft|abbr=on}}. 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 such as Asterias forbesi.{{cite journal |title=The spider crab Libinia emarginata Leach, 1815 (Decapoda Brachyura), and the starfish, an unsuitable predator but a cooperative prey |author=John C. Aldrich |journal=Crustaceana |volume=31 |issue=2 |year=1976 |pages=151–156 |jstor=20103088 |doi=10.1163/156854076X00189|bibcode=1976Crust..31..151A |s2cid=84785283 }}

Unusually for crabs, L. emarginata preferentially walks forwards, rather than sideways, although they are also capable of sidelong movement.{{cite journal |title=Muscular anatomy of the legs of the forward walking crab, Libinia emarginata (Decapoda, Brachyura, Majoidea) |author=A. G. Vidal-Gadea |author2=J. H. Belanger |name-list-style=amp |year=2009 |journal=Arthropod Structure & Development |volume=38 |issue=3 |pages=179–194 |doi=10.1016/j.asd.2008.12.002 |pmid=19166968|bibcode=2009ArtSD..38..179V }} Its skeletal,{{cite journal |author=A. G. Vidal-Gadea |author2=M. D. Rinehart |author3=J. H. Belanger |name-list-style=amp |year=2008 |title=Skeletal adaptation for sideways and forwards walking in three species of decapod crustaceans |journal=Arthropod Structure & Development |volume=37 |issue=2 |pages=95–108 |pmid=18089130 |doi=10.1016/j.asd.2007.06.002}} muscular and neural anatomy{{cite journal |author=Andrés G. Vidal-Gadea |author2=Jim H. Belanger |name-list-style=amp |year=2013 |title=The evolutionary transition to sideways-walking gaits in brachyurans was accompanied by a reduction in the number of motor neurons innervating proximal leg musculature |journal=Arthropod Structure & Development |volume=42 |issue=6 |pages=443–454 |doi=10.1016/j.asd.2013.07.003|pmid=23916868 |bibcode=2013ArtSD..42..443V }} 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.{{cite journal |author=R. E. DeGoursey |author2=P. J. Auster |name-list-style=amp |title=Aspects of a mating aggregation of the spider crab, Libinia emarginata |editor=M. A. Lang |editor2=W. C. Jaap |journal=Diving for Science…1989. Proceedings of the American Academy of Underwater Sciences Annual Scientific Diving Symposium 28 September – 1 October 1989 |publisher=Wood Hole Oceanographic Institution |location=Woods Hole, MA |year=1989 |url=http://archive.rubicon-foundation.org/10126|archive-url=https://archive.today/20130705002435/http://archive.rubicon-foundation.org/10126|url-status=usurped|archive-date=July 5, 2013}} 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.

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{{Taxonbar|from=Q5234006}}

Category:Majoidea

Category:Crabs of the Atlantic Ocean

Category:Crustaceans described in 1815

Category:Taxa named by William Elford Leach