Arthropoda
Limulus polyphemus
(Horseshoe Crab)
Size
Prosoma Width: 24-35cm (10-14") females; 13-21cm (5-8") males
Recognition Characters
There are three divisions to the body the prosoma, the opisthosoma, and the telson, commonly referred to as the cephalothorax, abdomen, and tail. Four eyes are located in 2 pairs on the dorsal front half of its shell and 5 light-receptor organs are beneath its shell. Horseshoe crabs have 6 pairs of legs. The first pincer-like pair are feeding legs; the next 4 pairs are walking-feeding legs; and the sixth and longest pair are solely walking legs used to clear away mud and silt during burrowing. Gills, located underneath the carapace consist of 5 overlaid flaps.
Color
Dark gray to brown
Habitat & Depth
Muddy and sandy bottoms offshore. Also bays and estuaries. To 30m.
Distribution at GRNMS
Rare. Only carapaces of dead individuals has been found under ledges or rocks.
Geographic Range
Atlantic Coast, from Nova Scotia to the Yucatan Peninsula, Gulf of Mexico
Behavior & Notes
Horseshoe crabs are nocturnal with activity peaking around the time of the full moon. They dig for food, such as worms, algae and mollusks in the sediment. During spring and summer, adults migrate in huge numbers towards sandy beaches and congregate in the shallow water to breed. The breeding is associated with the lunar and tidal cycles, with most adults arriving at the full or new moon and within a couple of hours of high tide. Wave direction guides the females towards the beach. Males patrol along the bottom of the beach in the shallow water, waiting to intercept beach-bound females. Pairs make their way to the high tide mark and the male fertilizes the eggs as they are laid into a 15 cm deep nest in the sand. From 2,000 - 20,000 eggs may be produced in a single clutch.
Synonyms