There is a remarkable primitive animal that lives in the Capeís shallow waters. It has survived the reign of the dinosaurs and continues today, 350 million years after it evolved. Its blue blood contains a substance capable of detecting bacterial endotoxins, and a shell with material that can increase the healing of wounds. It looks formidable but is harmless to humans. Indeed it has probably saved many human lives. It is, of course, the horseshoe crab (Limulus polyphemus), a common inhabitant of the Atlantic coast.
Horseshoe crabs are not true crabs. Instead they are more closely related to spiders, and that is easy to believe when one examines its underside morphology. There are five pairs of legs that enable the animal to crawl along the substrate where it feeds on worms and mollusks. There is a pair of small pincers called chelicerae which assist the animal in feeding, and a set of book gills used for breathing and swimming.
The shell or carapace of the animal is actually an exoskeleton. As the animal grows larger it needs to molt. It does this by splitting the carapace and emerging head first. True crabs molt from the back. Itís not unusual to find large numbers of recently molted shells on the Capeís beaches in late summer. It takes about twelve hours for the soft new shell to harden.
A female horseshoe crab will lay thousands of eggs during the spring full moon high tides. These are then fertilized by the smaller male and soon hatch out. In places such as Delaware Bay, horseshoe crabs are an important food source for thousands of migratory birds such as red knots and sanderlings. Without this essential food source many birds would not survive the long migration to northern grounds.
Recently horseshoe crab numbers along the east coast have declined. Many causes are suspect including coastal pollution, the lysate industry which uses the animalís blood, and even the taking of crabs for lobster traps. Several states have imposed restrictions on their harvesting, and some areas have been set aside to conserve horseshoe crab populations. Close monitoring and research is necessary to protect this important species. It would be a shame to lose an animal that has survived for millions of years.
Copyright Gil Newton 2009 Thanks to Chris Dumas for logo image.