Biomedical
Guides
Limulidae
Horseshoe Crabs
Limulidae is a family of marine arthropods comprising four extant species: Limulus polyphemus in North America and three Indo-Pacific species (Tachypleus tridentatus, T. gigas, and Carcinoscorpius rotundicauda). These organisms possess a distinctive horseshoe-shaped prosoma, long telson, and compound eyes. Populations are declining globally, with T. tridentatus classified as Endangered by the IUCN. The family is notable for its ancient evolutionary lineage and biomedical importance due to hemolymph containing endotoxin-sensitive coagulation factors.
Xiphosura
horseshoe crabs
Xiphosura is an order of marine chelicerate arthropods commonly known as horseshoe crabs. The group contains only four extant species, all within the family Limulidae. Xiphosurans first appeared in the fossil record approximately 480 million years ago and have retained a remarkably conserved body plan, earning them designation as living fossils. Recent phylogenomic studies have placed Xiphosura within Arachnida, often as the sister group to Ricinulei, though this classification remains under active revision. The order contains one extant suborder (Xiphosurida) and numerous extinct stem-genera.