Horseshoe Crab Horseshoe crabs are arthropods whose habitat is the ocean. Four species exist in the world today. They have an exoskeleton, a segmented body with three sections, jointed legs and a long sharp tail used for swimming. Most of the musculature of the horseshoe crab is found in middle segment or the main body. It has 113 distinct muscle groups and over 750 individual muscles used for walking, swimming and breathing through gills. Horseshoe crabs usually crawl on the bottom of the sea and they crawl to the seashore to reproduce. They also swim to the surface of the water by running and using their gills to move upward. They then use their long hard tail to turn over and they swim upside down.