Limulus

Limulus is a genus of horseshoe crabs in the family Limulidae. The best-known member is Limulus polyphemus, commonly called the Atlantic horseshoe crab, found along the Atlantic coast of North America and in parts of the Gulf of Mexico. Limulus species are ancient marine arthropods, with a fossil record dating back roughly 450 million years to the Ordovician period. The genus is one of several living groups of horseshoe crabs, with relatives in other genera such as Tachypleus and Carcinoscorpius.

Anatomy and biology are characteristic of horseshoe crabs. Limulus have a hard, dome-shaped carapace, a broad abdomen, and a long tail spine (telson). They possess book gills for respiration and a simple, two-part body plan that is well adapted to benthic life in shallow coastal waters. They are typically slow-moving, bottom-dwellers that feed on small invertebrates, detritus, and other organic matter found on the seafloor. Reproduction involves seasonal spawning on sandy beaches, with females often larger than males and releasing eggs that hatch into free-swimming larval stages.

Human uses and conservation concerns are notable. The blood of Limulus contains amebocytes used to produce Limulus amebocyte lysate, a biomedical test for bacterial endotoxins, which has created extensive harvesting of wild animals. This has raised conservation concerns, leading to management measures in some regions and the development of alternative endotoxin assays. Habitat loss, bycatch, and overharvesting pressure some populations, prompting monitoring and protective regulations in parts of the species’ range.