but the fossil genus Dibasterium had four pairs of branched walking legs. The pedipalps on a male change shape on their terminal molt, becoming boxing glove-like claspers that are used for grasping the female during mating. The last pair of legs for both male and female are the main legs used for pushing when walking on the ocean floor. The remaining leg pairs have a weak claw at the tip. Lost legs or the telson (tail) may slowly regenerate, and cracks in the body shell can heal. Behind its legs, the horseshoe crab has book gills, which exchange respiratory gases, and are also occasionally used for swimming. As in other arthropods, a true endoskeleton is absent, but the body does have an endoskeletal structure made up of cartilaginous plates that support the book gills. Growth Females are about 20–30% larger than males. The smallest species is C. rotundicauda and the largest is T. tridentatus. On average, males of C. rotundicauda are about long, including a tail (telson) that is about , and their carapace (prosoma) is about wide. Some southern populations (in the Yucatán Peninsula) of L. polyphemus are somewhat smaller, but otherwise this species is larger. In the largest species, T. tridentatus, females can reach as much as long, including their tail, and up to in weight. This is only about longer than the largest females of L. polyphemus and T. gigas, but roughly twice the weight. The juveniles grow about 33% larger with every molt until reaching adult size. Atlantic horseshoe crabs molt in late July. Diet Horseshoe crabs are more often found on the ocean floor searching for worms and molluscs, which are their main food. They may also feed on crustaceans and even small fish. Breeding During the breeding season (spring and summer in the Northeast U.S.; year-round in warmer locations or when the full moon rises), horseshoe crabs migrate to shallow coastal waters. The smaller male horseshoe crab clings to the back or opisthosoma of the larger female using specialized front claws and fertilizes the eggs as they are laid in the sand. Additional males called "satellite males" which are not attached to the female may surround the pair and have some success in fertilizing eggs. Young female horseshoe crabs can be identified by the lack of mating scars. The female can lay between 60,000 and 120,000 eggs in batches of a few thousand at