Procedure:

1. Draw the organism
2. Describe
3. Classify and use common name

Description:
The horseshoe crab has structural characteristics of both crustaceans and arachnids, and they are actually more closely related to spiders than crabs. The head and thorax are fused into the cephalothorax, which is covered by a hard, horseshoe-shaped shell. They have a compound eye on either side of this hard shell, and two simpler eyes between these two. They have pinchers (chelicerae) on either side of their mouths on the underside of the cephalothorax for catching prey. They have six pairs of walking legs, the last of which are rudimentary. On the underside of the abdomen has six additional pairs of appendages: the first covers the genital opening and the next five are modified as gills. The body and the appendages of the horseshoe crab are covered by a hard exoskeleton which consists of layers of chitin mixed with proteins. The exoskeleton is thickest around the head, where it protects the brain, but can be paper thin in other places such leg joints. To grow, the horseshow crab must shed its old exoskeleton periodically and grow a new one in a process called molting. Food for the horseshoecrab consists of small invertebrates. Female horseshoecrabs lay thier eggs in late spring in intertidal bays and estuaries. The horseshoe crabs are unique because they have remained virtually unchanged for the past 500 million years.