here are four species of horseshoe crabs, and all are members of the class Merostomata, aquatic animals with two body segments and a spikelike telson at the tail end. Perhaps the bestknown representative is Limulus polyphemus, the common horseshoe crab native to the northwest Atlantic coast and the Gulf of Mexico. These animals live in shallow water to depths of one hundred feet and prefer soft sand or mud bottoms, through which they slowly plow as they scavenge for food. Horseshoe crabs, unlike true crabs, do not have antennae. However, like crabs, they do have jointed appendages and a hard shell, or exoskeleton, made of chitin, which must be periodically shed to accommodate the growing body of the individual.
Horseshoe Crab Anatomy
The body of horseshoe crabs is divided into two segments: a large, helmet-shaped, forward section called the cephalothorax or prosoma, and a rear abdomen or opisthosoma, to which is attached the lancelike telson. Despite its threatening appearance, the telson is not used for defense, but rather for pushing and righting the body if the animal is overturned. There are two lateral and two median eyes on the upper surface of the prosoma. Although horseshoe crabs may be able to detect movement, there is little evidence that they can form images. The unique and relatively simple anatomy of horseshoe crab eyes make them favorite subjects for nervous system research. Under the cephalothorax there is a pair of small, pincerlike chelicerae, followed by five pairs of walking legs. The first four pairs are chelate and the fifth pair is for pushing away mud and silt during burrowing. The first four pairs also have spines along the joints closest to the body. These gnathobases are used to shred and macerate food and move it toward the mouth. The abdomen has six pairs of appendages, five of which are modified as thin, flaplike gills. In addition to providing oxygen to the animals, the gills function as paddles during upside-down swimming in small individuals.
Thanks for description - Animal life club