Horseshoe crabs are considered to be living fossils. Limulus, a genus found along the east coast of North America, has remained relatively unchanged since the Triassic Period about 220 million years ago. The North American species migrate to shallow water in the spring, then mate at night during high tide.

Everything you ever wanted to know about horseshoe crabs http://www.horseshoecrab.org/

Photographs and diagrams of living horseshoe crabs.

Horseshoe crabs feed on the sea bottom, capturing small molluscs and worms with their pincers. They break up hard material, such as mollusc shells, by grinding it between the hard edges of their upper legs or the gnathobases. The chelicerae, or the chilaria, small degenerate legs located behind the pusher legs, can push any food into the crab's mouth. A horseshoe crab also has a gizzard that contains sand and small bits of gravel to help grind its food.

 

 

In horseshoe crabs, fertilization is external. During the spring breeding season, in the North American species, thousands of the animals come ashore to breed in shallow water. Each male attaches to a female and is dragged around until she is ready to lay eggs. Young horseshoe crabs return to the water as free-swimming larvae.

 

Link to horseshoe crab research movie

Or use the following link.https://www.pbs.org/video/how-horseshoe-crabs-save-lives-3t9lsl/

Read the following webpage which describes the use of Horse shoe crabs in research

On web page reference is made to obtaining blood from the pericardial cavity.