{{Short description|Species of crustacean}} {{Speciesbox | name = ''Libinia emarginata'' | image = Libinia emarginata.png | genus = Libinia | species = emarginata | authority = Leach, 1815&nbsp;<ref>{{ITIS |id=98455 |taxon=''Libinia emarginata'' Leach, 1815 |accessdate=November 13, 2011}}</ref> | synonyms = ''Libinia canaliculata'' <small>Say, 1817</small> | synonyms_ref = &nbsp;<ref name="Ng">{{cite journal|journal=Raffles Bulletin of Zoology |year=2008 |volume=17 |pages=1–286 |title=Systema Brachyurorum: Part I. An annotated checklist of extant Brachyuran crabs of the world |author=Peter K. L. Ng |author2=Danièle Guinot |author3=Peter J. F. Davie |name-list-style=amp |url=http://rmbr.nus.edu.sg/rbz/biblio/s17/s17rbz.pdf |url-status=dead |archive-url=https://web.archive.org/web/20110606061453/http://rmbr.nus.edu.sg/rbz/biblio/s17/s17rbz.pdf |archive-date=2011-06-06 }}</ref> }}

'''''Libinia emarginata''''', the '''portly spider crab''', '''common spider crab''' or '''nine-spined spider crab''', is a species of stenohaline crab that lives on the Atlantic coast of North America.

==Distribution== ''Libinia emarginata'' occurs from Nova Scotia to the Florida Keys and through the Gulf of Mexico.<ref>{{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 }}</ref> It lives at depths of up to {{convert|160|ft|abbr=on}}, with exceptional records of up to {{convert|400|ft|abbr=on}}.<ref name="Martinez"/>

==Description== ''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}}.<ref name="Martinez"/> The whole crab is khaki, and the carapace is covered in spines and tubercles,<ref name="Lippson">{{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 }}</ref> and, as with other decorator crabs, often clothes itself in debris and small invertebrates.<ref name="Martinez"/>

===Reproduction=== thumb|left|A mating aggregation of ''L.&nbsp;emarginata'' 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.<ref name="Hirsch">{{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 }}</ref>

==Similar species== ''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.&nbsp;emarginata'' there are nine, while in ''L.&nbsp;dubia'' there are only six.<ref name="Lippson"/> Also, the rostrum of ''L. dubia'' is more deeply forked than that of ''L.&nbsp;emarginata''.<ref name="Martinez">{{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}}</ref>

==Ecology and behavior== ''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.<ref name="Lippson"/>

Despite its small size, in comparison to other predatory crabs, ''L. emarginata'' feeds on large starfish such as ''Asterias forbesi''.<ref>{{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 }}</ref>

Unusually for crabs, ''L.&nbsp;emarginata'' preferentially walks forwards, rather than sideways, although they are also capable of sidelong movement.<ref name="Vidal09">{{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 }}</ref> Its skeletal,<ref>{{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}}</ref> muscular<ref name="Vidal09"/> and neural anatomy<ref>{{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 }}</ref> more closely resembles that of forward-walking species, rather than that of more closely related sideways-walking species.

''L.&nbsp;emarginata'' will mate in large aggregations.<ref name=RRR10126>{{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}}</ref> These aggregations may function as a protective mechanism during reproduction.<ref name=RRR10126/> Males of ''L.&nbsp;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.<ref name="Hirsch"/>

==References== {{Reflist|32em}}

{{Taxonbar|from=Q5234006}}

Category:Majoidea Category:Crabs of the Atlantic Ocean Category:Crustaceans described in 1815 Category:Taxa named by William Elford Leach