Temporal range: Earliest Hirnantian–Present, 445–0 Ma
PreꞒ
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S
D
C
P
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Restoration of Lunataspis, the oldest known xiphosuran
The extant Atlantic horseshoe crab (Limulus polyphemus)
Scientific classification
Domain:
Eukaryota
Kingdom:
Animalia
Phylum:
Arthropoda
Subphylum:
Chelicerata
Clade:
Prosomapoda
Order:
Xiphosura Latreille, 1802
Groups
†Lunataspis[1]
†Maldybulakia
†Willwerathia
†Kasibelinuridae
Xiphosurida
†Belinurina
Limulina
Xiphosura (/zɪfoʊˈsjʊərə/;[2] from Ancient Greek ξίφος (xíphos) 'sword', and οὐρά (ourá) 'tail', in reference to its sword-like telson) is an order of arthropods related to arachnids. They are more commonly known as horseshoe crabs (a name applied more specifically to the only extant family, Limulidae). They first appeared in the Hirnantian (Late Ordovician). Currently, there are only four living species. Xiphosura contains one suborder, Xiphosurida, and several stem-genera.
The group has hardly changed in appearance in hundreds of millions of years; the modern horseshoe crabs look almost identical to prehistoric genera and are considered to be living fossils. The most notable difference between ancient and modern forms is that the abdominal segments in present species are fused into a single unit in adults.
Xiphosura were historically placed in the class Merostomata, although this term was intended to encompass also the eurypterids, whence it denoted what is now known to be an unnatural (paraphyletic) group (although this is a grouping recovered in some recent cladistic analyses).[3] Although the name Merostomata is still seen in textbooks, without reference to the Eurypterida, some have urged that this usage should be discouraged.[4] The Merostomata label originally did not include Eurypterida, although they were added in as a better understanding of the extinct group evolved. Now Eurypterida is classified within Sclerophorata together with the arachnids, and therefore, Merostomata is now a synonym of Xiphosura.[5] Several recent phylogenomic studies place Xiphosura within Arachnida, often as the sister group of Ricinulei; included among them are taxonomically comprehensive analyses of both morphology and genomes, which have recovered Merostomata as a derived clade of arachnids.[6][7][8]
^Cite error: The named reference Lamsdell2020 was invoked but never defined (see the help page).
^"Xiphosuran". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
^Garwood, Russell J.; Dunlop, Jason A. (2014). "Three-dimensional reconstruction and the phylogeny of extinct chelicerate orders". PeerJ. 2: e641. doi:10.7717/peerj.641. PMC 4232842. PMID 25405073.
^H. B. Boudreaux (1979). Arthropod Phylogeny with Special Reference to Insects. John Wiley & Sons. pp. 1–320.
^Lamsdell, James C. (2012-12-18). "Revised systematics of Palaeozoic 'horseshoe crabs' and the myth of monophyletic Xiphosura". Zoological Journal of the Linnean Society. 167 (1): 1–27. doi:10.1111/j.1096-3642.2012.00874.x. ISSN 0024-4082.
^Sharma, Prashant P.; Ballesteros, Jesús A. (14 February 2019). "A Critical Appraisal of the Placement of Xiphosura (Chelicerata) with Account of Known Sources of Phylogenetic Error". Systematic Biology. 68 (6): 896–917. doi:10.1093/sysbio/syz011. PMID 30917194.
^Ballesteros, Jesús A.; Santibáñez López, Carlos E.; Kováč, Ľubomír; Gavish-Regev, Efrat; Sharma, Prashant P. (2019-12-18). "Ordered phylogenomic subsampling enables diagnosis of systematic errors in the placement of the enigmatic arachnid order Palpigradi". Proceedings of the Royal Society B: Biological Sciences. 286 (1917): 20192426. doi:10.1098/rspb.2019.2426. ISSN 0962-8452. PMC 6939912. PMID 31847768.
^Ballesteros, Jesús A; Santibáñez-López, Carlos E; Baker, Caitlin M; Benavides, Ligia R; Cunha, Tauana J; Gainett, Guilherme; Ontano, Andrew Z; Setton, Emily V W; Arango, Claudia P; Gavish-Regev, Efrat; Harvey, Mark S; Wheeler, Ward C; Hormiga, Gustavo; Giribet, Gonzalo; Sharma, Prashant P (2022-02-03). Teeling, Emma (ed.). "Comprehensive Species Sampling and Sophisticated Algorithmic Approaches Refute the Monophyly of Arachnida". Molecular Biology and Evolution. 39 (2): msac021. doi:10.1093/molbev/msac021. ISSN 0737-4038. PMC 8845124. PMID 35137183.
Xiphosura (/zɪfoʊˈsjʊərə/; from Ancient Greek ξίφος (xíphos) 'sword', and οὐρά (ourá) 'tail', in reference to its sword-like telson) is an order of arthropods...
arthropods of the family Limulidae and the only living members of the order Xiphosura. Despite their name, they are not true crabs or crustaceans: they are...
scorpions) and the extant Xiphosura (horseshoe crabs). The term was originally used by James Dwight Dana to refer to Xiphosura only, but was emended by...
appendages form spinnerets that extrude silk, while those of horseshoe crabs (Xiphosura) form gills. Like all arthropods, chelicerates' bodies and appendages...
include Limulus cyclops, Xiphosura americana, and Polyphemus occidentalis. It is the tail that earns this order its name Xiphosura, which derives from the...
Chelicerata Order: Xiphosura Family: Limulidae Genus: Limulus O. F. Müller, 1785 Type species Monoculus polyphemus Linnaeus, 1758 Synonyms Xiphosura...
identified as the group labelled "Euchelicerata".) A 2019 analysis nests Xiphosura deeply within Arachnida. Discovering relationships within the arachnids...
Prosomapoda is a clade of euchelicerates including the groups Xiphosura (horseshoe crabs) and Planaterga (a group comprising bunodids, pseudoniscids,...
The largest animal currently alive is the blue whale. The maximum recorded weight was 190 tonnes for a specimen measuring 27.6 metres (91 ft), whereas...
The Solnhofen Plattenkalk, a collective term of multiple Late Jurassic lithographic limestones in southeastern Germany, is famous for its well preserved...
on the relationships within the Xiphosura and the relations to other closely related groups concluded that the Xiphosura, as presently understood, was paraphyletic...
and the Opiliones, as well as in non-arachnid Chelicerata such as the Xiphosura and Eurypterida.[citation needed] The chelifores of the Pycnogonida may...
chelae in most of these groups may not be homologous with those found in Xiphosura. The pedipalps are distinctly raptorial (i.e., modified for seizing prey)...
The El Mers Group is a geological group in the Middle Atlas of Morocco. It is subdivided into three formations named the El Mers I, II, and III Formations...
Mikulic, DG; Kluessendorf, J (2005). "A new synziphosurine (Chelicerata: Xiphosura) from the Late Llandovery (Silurian) Waukesha Lagerstatte, Wisconsin,...
crab species, Tachypleus tridentatus and Carcinoscorpius rotundicauda (Xiphosura), in Hong Kong with a regional Asian comparison". Journal of Natural History...
Shpinev; D. V. Vasilenko (2018). "First fossil xiphosuran (Chelicerata, Xiphosura) egg clutch from the Carboniferous of Khakassia". Paleontological Journal...
analysis in early 2019 suggested the sister group of the ricinuleids may be Xiphosura, the arthropod order containing horseshoe crabs. In response to this work...
Arthropods are invertebrate animals having an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They...
crabs (Xiphosura). It was later identified as a grade composed of various basal euchelicerates, eventually excluded from the monophyletic Xiphosura sensu...
Ballesteros, Jesús A. (2019). "A Critical Appraisal of the Placement of Xiphosura (Chelicerata) with Account of Known Sources of Phylogenetic Error". Systematic...
systematics of Palaeozoic 'horseshoe crabs' and the myth of monophyletic Xiphosura". Zoological Journal of the Linnean Society. 167 (1): 1–27. doi:10.1111/j...
Long Island Sound is a large marine estuary in the Northeastern United States. It forms the maritime border between New York's Long Island and Connecticut...
(2019-11-01). Halanych, Ken (ed.). "A Critical Appraisal of the Placement of Xiphosura (Chelicerata) with Account of Known Sources of Phylogenetic Error". Systematic...
Evolution: What the Fossils Say and Why It Matters by Donald R. Prothero and Carl Buell Xiphosura at Palaeos.com Paleontology portal v t e v t e v t e...
Chasmataspidida. Chasmataspidids are probably related to horseshoe crabs (Xiphosura) and/or sea scorpions (Eurypterida), with more recent studies suggest...
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