Xiphosura 1093073 215270910 2008-05-27T13:35:52Z Mani1 86923 interwiki Persian {{Taxobox | name = Xiphosura | image = Limulus_polyphemus.jpg | regnum = [[Animal]]ia | phylum = [[Arthropod]]a | subphylum = [[Chelicerata]] | classis = [[Xiphosura]] | subdivision_ranks = Orders | subdivision = Synziphosurida <br> Xiphosurida }} '''Xiphosura''' is a [[class (biology)|class]] of marine [[Chelicerata|chelicerates]] which includes a large number of extinct lineages and only four recent species in the family [[Limulidae]], which include the [[horseshoe crab]]s. The group has hardly changed in millions of years; the modern horseshoe crabs look almost identical to prehistoric genera such as the [[Jurassic]] ''[[Mesolimulus]]'', and are considered to be [[living fossil]]s. Xiphosura are typically placed the class [[Merostomata]], comprising also the [[Eurypterida|eurypterids]], but this traditional usage in the past reflected the acceptance of an unnatural ([[paraphyly|paraphyletic]]) group. Although the name Merostomata can be seen in some textbooks, without reference to the Eurypterida, some individuals have urged that this usage should be discouraged (e.g. Boudreaux, 1979). ==Size== Minimum adult body size in [[Paleozoic]] species is 1-3 cm. Recent species may attain 60 cm. <!-- Image with disputed fair-use status removed: [[Image:Limulus-appendages.jpg|left|thumb|400px|Diagram of appendages of ''Limulus polyphemus'', chelicerae in red, prosomal appendages I-V in shades of orange, opisthosomal appendages (opercles) in shades of yellow and the chilaria in purple.]] --> ==Characterization== Body covered with heavy mineralized cuticle, divided into anterior [[prosoma]] and posterior [[opisthosoma]], this carrying a [[caudal spine]] (also referred to as a [[telson]], though this same term is also used for a different structure in crustaceans). Prosoma dorsally covered by semicircular [[carapace]] which may bear eyes (median ocelli and lateral compound eyes) and ventrally the walking legs and [[chelicera]]e. Coxae of legs carry [[gnathobase]]s performing mastication. Reduced appendages of absorbed first opisthosomal segment can still be seen as a sixth pair of small legs called [[chilaria]]. Opisthosoma divided into mesosoma, with flattened appendages and metasoma (posterior) without appendages. Mesosoma may have all segments fused forming a [[thoracetron]]. ==Ecology== Recent Xiphosura are marine [[benthos|benthic]] living on soft substrate, coming ashore for reproduction. Based on the sediment associations, it was proposed that Paleozoic species were not marine, but lived in fresh water and brackish water. ==Taxa removed from Xiphosura== There are two groups originally included in the Xiphosura, but which have been assigned to separate classes: * [[Aglaspida]] Walcott 1911 (Cambrian to Ordovician). * [[Chasmataspida]] Caster & Brooks, 1956 (Lower Ordovician). ==Classification of the Xiphosura== Class Xiphosura Latreille, 1802 * †Order Synziphosurida ** Weinberginidae Richter and Richter, 1929 (Lower [[Devonian]]) ** Bunodidae Packard 1886 *** Bunodinae Packard 1886 (Upper [[Silurian]] to Downtonian) *** Limuloidinae Størmer, 1952 (Upper Silurian) ** Pseudoniscidae Packard 1886 (Upper Silurian) ** Kasibelinuridae Pickett, 1993 (Middle Devonian to Late Devonian) * Order Xiphosurida ** †Suborder Bellinurina *** Elleriidae Raymond, 1944 (Upper Devonian to Upper [[Carboniferous]]) *** Euproopidae Eller, 1938 (= Liomesaspidae Raymond 1944) (Upper Carboniferous to Lower Permian) *** Bellinuridae Zittel and Eastman, 1913 (Middle Devonian to Upper Carboniferous) ** Suborder Limulina *** †Rolfeiidae Selden and Siveter, 1987 (Early Carboniferous to Early Permian) *** †Paleolimulidae Raymond, 1944 (Carboniferous to Permian) *** †Moravuridae Pribyl, 1967 ([[Mississippian]]) *** †Austrolimulidae + †Heterolimulidae (Middle [[Triassic]]) *** Limulidae Zittel, 1885 **** †Mesolimulinae Størmer, 1952 (Lower Triassic to [[Cretaceous]]) **** Limulinae Zittel, 1885 ***** Tachypleini Pocock, 1902 ([[Miocene]] to '''Recent''') ***** Limulini Zittel, 1885 ('''Recent''') ==References== *Anderson, L. I. and P. A. Selden. 1997. Opisthosomal fusion and phylogeny of Palaeozoic Xiphosura. Lethaia 30:19-31. * Boudreaux H. B., 1979. Arthropod phylogeny with special reference to insects. John Willey & sons, New York, Chichester, Brisbane, Toronto. 320 pp. * Brusca, R. C. & Brusca, G. J. (2002) Invertebrates. Sinauer Associates, Massachusetts. 880 pages, 615 illustrations. * Dunlop, J. A. 1997. Palaeozoic arachnids and their significance for arachnid phylogeny. Proceedings of the 16th European Colloquium of Arachnology, 65-82 * Dunlop, J.A.; Selden, P.A. 1997: The Early History and Phylogeny of the Chelicerates. In Fortey, R.A.; Thomas, R.H. (eds.) 1997: Arthropod Relationships. Systematics Association Special Volume Series 55, pp. 221-235. * Rohdendorf B.B. (editor), Fundamentals of Paleontology, vol. 9, Arthropoda-Tracheata and Chelicerata: 894 pp. [1991 English translation of Russian original, Smithsonian Institution Libraries and National Science Foundation]. * Snodgrass, R.E., 1952. A textbook of arthropod anatomy. Hafner Publishing Company, New York. ==External links== *[http://www.peripatus.gen.nz/Taxa/Arthropoda/Index.html Peripatus] - an overview of arthropod relationships. *[http://www.palaeos.com/Invertebrates/Arthropods/Chelicerata/Merostomata/Xiphosura.html Paleos] - a site with a synoptic account of the Xiphosura, focused on fossils. {{Arthropods}} [[Category:Arthropods]] [[Category:Xiphosura| ]] [[ca:Xifosur]] [[fa:شمشیردمان]] [[ru:Мечехвосты]]