Xiphosura


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Related to Xiphosura: Limulidae, Merostomata, Symphyla, Eurypterids

Xiphosura

[‚zif·ə′su̇r·ə]
(invertebrate zoology)
The equivalent name for Xiphosurida.

Xiphosura

 

an order of predominantly extinct marine arthropods of the class Merostomata. The compact body, which may reach a length of 90 cm, consists of an unsegmented prosoma with six pairs of appendages that serve for locomotion, food-getting, and mastication, as well as an abdomen with a caudal spine and six pairs of leaf-shaped limbs bearing numerous branchial leaflets. There is a pair of simple eyes on the dorsal side of the prosoma and a lateral pair of compound eyes. Xiphosurans are dioecious. In the egg, which is deposited in sand, the embryo passes through a protaspid stage of development similar to that of the trilobites. A trilobite larva emerges from the egg.

Twelve fossil genera of Xiphosura are known from the Silurian; they differ from extant species in that their abdomens are somewhat segmented. There are three genera of extant xiphosurans, including five tropical species: one species is found along the Atlantic coasts of Central and North America; the others are encountered off the southeastern and eastern coasts of Asia and neighboring islands. Xiphosurans live in shallows, crawling along the bottom; they can easily shovel their way into the bottom and can swim, with their ventral side up, by means of the abdominal limbs. They feed on mollusks and other benthic invertebrates and, sometimes, on algae. In America and Japan, xiphosurans are commercially valuable (they are used as fertilizer).

IA. A. BIRSHTEIN

References in periodicals archive ?
Molecular phylogeny of extant horseshoe crabs (Xiphosura, Limulidae) indicates Paleogene diversification of Asian species.
Opisthosomal fusion and phylogeny of Palaeozoic Xiphosura. Lethaia 30:19-31.
Group Paleozoic Mesozoic Cenozoic Total Pycnogonida 6 3 -- 9 "Euchelicerata" 5 -- -- 5 Xiphosura 75 20 1 96 Chasmataspidida 8 -- -- 8 Eurypterida 241 -- -- 241 Scorpiones 79 16 16 111 Opiliones 7 1 17 25 Phalangiotarbida 30 -- -- 30 Pseudoscorpiones 1 2 35 38 Solifugae 2 1 2 5 Acari: Anactinotrichida -- 1 10 11 Acari: Actinotrichida 15 15 253 283 Palpigradi -- -- 1 1 Ricinulei 15 -- -- 15 "Pantetrapulmonata" 3 -- -- 3 Trigonotarbida 71 -- -- 71 Araneae 18 31 930 979 Haptopoda 1 -- -- 1 Amblypygi 5 1 3 9 Uropygi 6 1 -- 7 Schizomida -- -- 4 4 all Chelicerata 588 92 1272 1952 Arachnida only 253 69 1271 1593 Table 2.--Significant localities yielding fossil Chelicerata referred to in the text, including details of their stratigraphic position and approximate age in millions of years (Ma).
Evolution of arthropod visual systems: development of the eyes and central visual pathways in the horseshoe crab Eimulus polyphemus Linnaeus, 1758 (Chelicerata, Xiphosura).
On the fine structure of spermatozoa of Tachypleus gigas (Xiphosura, Merostomata).
Tachypleus tridentatus (Xiphosura), on a nursery beach at Shui Hau Wan, Hong Kong.
However, participation in formation of the mesodermal components of the gut is apparently unique to the Xiphosura. If, as suggested here, some yolk nuclei cellularize and differentiate as amebocytes during late embryogenesis, it would suggest that retention of large numbers of yolk nuclei in horseshoe crab embryos provides the embryos with a pool of undeterm ined nuclei that can be utilized in a variety of distinct tissues during development.