Horseshoe crab

Characteristics

These animals have a hard, rounded carapace, a jointed underside with multiple pairs of legs, and a long, pointed telson (tail spine) used for righting themselves. They breathe with book gills and possess copper-based blood that is blue in color; the blood contains clotting cells important to biomedical testing. Well-known species include Limulus polyphemus and several Asian species.

• Domed carapace and dorsal shield
• Telson (tail spine) for maneuvering
• Book gills for respiration and locomotion on the seafloor
• Blue hemolymph used in medical assays (Limulus polyphemus)

Habitat and behaviour

Horseshoe crabs are primarily benthic: they crawl on sandy or muddy bottoms in shallow coastal waters and estuaries. Typical habitats include sheltered bays and tidal flats. Many populations come ashore at high tides to spawn on sandy beaches and river mouths, linking marine and shoreline ecosystems (coastal, intertidal, estuarine).

Life cycle and ecological role

Spawning usually occurs in seasonal, often nocturnal, mass events. Females deposit thousands of eggs in nests on beaches; eggs provide a critical food resource for migrating shorebirds and other coastal wildlife. Juveniles hatch as small, trilobite-like larvae and grow through a series of molts before reaching adult form.

Uses, importance and conservation

Horseshoe crabs play a dual role: they are keystone ecological species in many coastal food webs and a source of biomedical material—cells from their blood are used to detect bacterial endotoxins. At the same time they are harvested for bait and biomedical use, and face threats from habitat loss, coastal development and climate change. Conservation efforts include regulated harvests, monitoring, and research into synthetic alternatives to reduce pressure on wild populations.

For more detailed information, see species accounts and conservation resources linked to taxonomic and habitat references (species overview, common name note, taxonomic context).