Limulus polyphemus

Limulus polyphemus, commonly known as the Atlantic horseshoe crab, is a marine chelicerate found along the Atlantic coasts of North America and the Gulf of Mexico. Despite its name, it is not a true crab, but belongs to a separate subphylum of arthropods.

Taxonomy

The species was first described by Carl Linnaeus in 1758. It is the most well-known of the four extant species of horseshoe crabs. The genus name Limulus means "askew", while polyphemus refers to Polyphemus, a giant cyclops from Greek mythology, an allusion to the animal's large, compound eyes.

Description

Adult Limulus polyphemus can reach sizes up to 60 cm in length (including tail), with a greenish dark grey color. The body is divided into two main parts: a frontal section known as the prosoma, and a rear section, the opisthosoma. The tail, or telson, is long and pointed. The most notable features are the two large, compound eyes, as well as several smaller, simple eyes.

Habitat and distribution

Limulus polyphemus is found along the Atlantic coasts of North America, from Maine to the Gulf of Mexico. It prefers shallow, sandy or muddy coastal habitats, and can often be found in estuaries and bays.

Behavior and ecology

The Atlantic horseshoe crab is primarily nocturnal and an opportunistic feeder, consuming a variety of invertebrates. During the breeding season, females come ashore to lay eggs, which are then fertilized by males. The eggs are a crucial food source for migrating shorebirds.

Importance to humans

The blood of Limulus polyphemus is used in the Limulus amebocyte lysate (LAL) test, which is crucial for detecting bacterial endotoxins in medical applications. The species is also harvested as bait for eel and conch fisheries.

Conservation

Limulus polyphemus is currently listed as Vulnerable by the IUCN Red List. Threats include habitat loss, overharvesting for bait, and biomedical bleeding.