Xiphosura

Xiphosura [‚zif·ə′su̇r·ə]

(invertebrate zoology)

The equivalent name for Xiphosurida.

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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