Carcinoscorpius rotundicauda 

Horseshoe crabs are found in shallow water on soft sandy bottoms.

Horseshoe crabs were formerly harvested for use as fertilizer. Currently they are harvested for their blood, which contains a chemical called Limulus Amoebocyte Lysate (LAL) that is used to detect pathogens and their endotoxins, and used as bait for the eel and conch fisheries.

The entire body of horseshoe crab is protected by a hard, dark brown carapace. They have two large compound eyes and multiple smaller simple ones atop the carapace. Beneath the carapace they look quite similar to a large spider. They have five pairs of legs for walking, swimming and moving food into the mouth. Behind their legs, they have book gills, which exchange respiratory gases and are also occasionally used for swimming.

While they can swim upside down, they usually are found on the ocean floor searching for worms and mollusks, which are their main food. They may also feed on crustaceans and even small fish.

In the spring, Horseshoe crabs migrate to certain shallow coastal waters. Males select a female and cling onto her back. The female digs a hole in the sand and lays her eggs while the male fertilizes them. The female can lay between 60,000-120,000 eggs in batches of a few thousand at a time. The eggs take about 2 weeks to hatch. The larvae continue to molt six times during the first year. It takes 11 years to reach sexual maturity, after which they may live up to 14 more years.

1. Limulidae (n.d.). Retrieved December 12, 2007, from http://en.wikipedia.org/wiki/Limulidae

http://www.catalogueoflife.org/
http://www.iucnredlist.org/search/details.php/3856/all