Atlantic horseshoe crab
The Atlantic horseshoe crab, scientifically known as Limulus polyphemus, is a unique marine animal distinguished by its horseshoe-shaped carapace and crab-like features. Despite its name, it is not a true crab but is more closely related to spiders and scorpions. Typically found along the Atlantic coast of North America, from the Gulf of Maine to the Gulf of Mexico, this species thrives in sandy or muddy seabeds at depths of around 75 feet. The Atlantic horseshoe crab can grow to lengths of 1 to 2 feet, with females generally larger than males.
These creatures are scavenging carnivores, feeding on invertebrates, mollusks, and sometimes algae, using their specialized mouthparts to capture and consume prey. Notably, during mating season, males gather with females in intertidal zones, where females lay thousands of eggs in sand depressions. The eggs hatch into tiny larvae after several months, and it takes about three years for them to reach maturity. While the Atlantic horseshoe crab can live up to 25 years, it faces threats from overharvesting and habitat loss, leading to its classification as a vulnerable species.
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Horseshoe crab
The Atlantic horseshoe crab gets its name from its horseshoe-shaped carapace, or shell, and its crab-like body, legs, and pinchers. In spite of its name, the Atlantic horseshoe crab is not closely related to other crabs. Actually, the Atlantic horseshoe crab is more closely related to spiders and scorpions because of its pincher-like mouthparts.
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Merostomata
Order: Xiphosura
Family: Limulidae
Genus: Limulus
Species: Polyphemus
The Atlantic horseshoe crab is typically found along the Atlantic coast of North America from the Gulf of Maine to the Gulf of Mexico. This species of horseshoe crab, Limulus polyphemus, is the one of four species of horseshoe crab. It is the only species to inhabit the waters around North America. The other three species are found in the Pacific from Japan to the Philippines.
The Atlantic horseshoe crab spends its time on sand or mud flats. It is often found at depths of about 75 feet (22 1/2 meters). It burrows into the seabed with its legs while driving its head forward into the sand. Buried under the sand, only the Atlantic horseshoe crab's eyes are visible.
The Atlantic horseshoe crab typically grows to a length of about one to 2 feet (30 to 60 centimeters) with the female typically being slightly larger than the male. This creature gets its unusual name from the large, rounded, horseshoe-shaped carapace, or shell, which covers its legs and softer body parts.
The Atlantic horseshoe crab's carapace is divided into two parts: the dorsal plate and the opisithosoma. The dorsal plate is the rounded front piece. This covers the Atlantic horseshoe crab's five pairs of jointed legs and chelicerae, or mouthparts. Behind the dorsal plate is the Atlantic horseshoe crab's opisithosoma. This part is flatter than the dorsal plate and slopes toward the Atlantic horseshoe crab's caudal spine, or tail. This part of the carapace protects the Atlantic horseshoe crab's reproductive organs, digestive system, and respiratory, or breathing, organs.
At the base of the opisithosoma is the Atlantic horseshoe crab's caudal spine. This piece is a long, pointed spine which helps the Atlantic horseshoe crab move along the sand. The spine, working along with the Atlantic horseshoe crab's five pairs of walking legs, helps it to dig into the seabed and shuffle along the beach. The spine also helps the crab turn over if it settles belly-up in the sand.
The Atlantic horseshoe crab is usually a scavenging carnivore. This means it searches through the sea for fleshy food. Typically, the Atlantic horseshoe crab lives on a diet of invertebrates, mollusks, worms, and shellfish. It may sometimes eat algae. It uses the jaw-like pinchers at the ends of each of its jointed legs to catch and tear its prey.
After catching its prey, the Atlantic horseshoe crab chews its catch with its pincher-like mouthparts. Although the Atlantic horseshoe crab is called a crab, the shape of its mouthparts shows that it is actually more closely related to spiders and scorpions.
Many male and female Atlantic horseshoe crabs gather at night in intertidal zones for mating. The process begins when female Atlantic horseshoe crabs start to lay their eggs. When this happens, male Atlantic horseshoe crabs crawl on top of the females to fertilize the eggs as they are being laid. A single Atlantic horseshoe crab may lay between 15,000 and 64,000 eggs. She lays these eggs in a deep depression in the sand and covers them once they all are fertilized. Many months later the eggs hatch as tiny larvae. Larval horseshoe crabs are typically about 1/3 of an inch (one centimeter) long. It takes about three years for the young to develop into mature Atlantic horseshoe crabs.
Sharks, fish, turtles, and birds may prey upon the Atlantic horseshoe crab. The life span of the Atlantic horseshoe crab may be up to 25 years. Overharvesting and habitat loss have made the Atlantic horseshoe crab a vulnerable species.
Bibliography
“Natural History: The Amazing Horseshoe.” The Horseshoe Crab, 2011, www.horseshoecrab.org/nh/species.html. Accessed 11 Apr. 2024.
Smithsonian Institution. “10 Incredible Horseshoe Crab Facts - Smithsonian's National Zoo and Conservation Biology Institute.” National Zoo, 3 June 2022, nationalzoo.si.edu/animals/news/10-incredible-horseshoe-crab-facts. Accessed 11 Apr. 2024.