Horsefoot Crab-The Living Fossil

Horsefoot Crab-The Living Fossil
1. The name derives from "Horsefoot Crabs" so called because of the resemblance of the shell to a horse hoof.

2. Its name refers to the horseshoe shape of the largest part of its shell.

3. Because it has remained almost unchanged for millions of years, the Horseshoe Crab is often called a “Living Fossil”.  The Horseshoe Crab is one of the Earth’s oldest creatures, appearing over 350 million years before the dinosaurs!

4. Horseshoe Crabs are well known for their highly visible mating activities and habits. The peak in spawning activity usually coincides with the full moon and evening spring tides. Adults prefer beaches, bays and coves which are protected from rough water.

5. The horseshoe crab is not actually a true crab, but a member of an ancient group of arthropods, closely related to spiders and scorpions.

6. The horseshoe crab has three divisions of its body-the prosoma (cephlathorax), the opisthosoma (abdomen) and the telson (tail).

7. The horseshoe crab has 10 eyes. There are two compound eyes visible on top of their shell that helps locate mates. In addition, each animal has eight other “eyes” located elsewhere on the prosoma, tail and underside of the body. These eyes sense visible and ultraviolet light, which are believed to allow the animal to respond to day,night and lunar cycles.

8. Although it looks menacing, the tail is not used as a weapon. It is used to plow through muck and sand, to act as a rudder when steering itself and to right itself when it flips on its back.

9. The mouth is located at the center of the underside of its body amongst its five pairs of walking legs.

10. The males can be distinguished from the females by the first pair of legs, which terminate in a hook-shaped structure used to grasp the shell of the female during mating. The females also are significantly larger than the male at maturity.

11. Horseshoe crabs undergo about 16 molts until they are full-grown (at nine to12 years). Most molting occurs during their first three years and then about once a year thereafter. Once mature, individuals do not molt again. Females can reach a width of 12 inches. Males are somewhat smaller.

12. The horseshoe crab’s blood is blue (caused by the presence of hemocyanin; human blood is red because of the presence of hemoglobin), and it has unique bacteria-fighting abilities. It is used by pharmaceutical and biomedical industries for important medical research and testing.

13. The blood also contains a number of compounds that bind to inactivate bacteria, fungi and viruses, functioning as a primitive "immune" system. An extract of horseshoe crab blood is used by the pharmaceutical and medical device industries to test their products for bacterial contamination.

14. Horseshoe Crabs come to spawn on the high tide of the new and full moon in late spring and early summer. 

15. They require a sloping sandy beach to lay their eggs.

16. It takes 9-12 years for a Horseshoe Crab to reach maturity, so all the Horseshoe Crabs you see on the beach are at least 9 years old and have a life span of 16-40  years.

17. The Crabs grow by molting or shedding and emerge 25% larger with each molt. Molting occurs several time during the first two to three years and about once a year there after.  After 16 molts (usually between 9 and 12 years) they will be fully grown adults. Females reach maturity 1 year later than males and consequently, go through an additional molt.

18. Mature Crabs  then  repeat what has occurred for years, an annual spring migration to inshore spawning  areas.They spend their life in the deeper water and when they reach maturity, the females move to the beaches only to spawn.

19. The female, carrying the male, moves up on the beach, buries herself and lays 20,000-60,000 eggs, the male then fertilizes the eggs. Many of the eggs are eaten by birds and others animals and there is also a good chance of stranding on the beach. Single males that don’t find a female crowd around the mating pairs on the beach trying to fertilize some of the eggs.

20. Adults males are two-thirds the size of the females and have a modified front pincher to attach to the female to mate. The body is sometimes two feet long.  Alive, it is brownish-green in color.  After it dies, the adult is dark brown. They breathe by means of gills attached to the underside of the last pair of abdominal legs.

21. The Horseshoe Crab can swim upside down in the ocean.

22. The Horseshoe Crab’s mouth, located on the under body and is surrounded by its legs and, while harmless, it is advisable to handle these Crabs with care or not at all. The Crabs feed mostly at night and burrow for worms and mollusks. However, they will feed at any time.

23. The Horseshoe Crab’s tail, while scary, is not a weapon. The tail is used to plow the crab through the sand and muck, to act as a rudder and to right the crab up when it accidentally tips over.  If they cannot get turned back over, they will die.

24. Horseshoe Crabs have 2 compound eyes on the top of their shell with a sight range of about 3 feet. By  recording electrical impulses from the crab’s optic nerve in its lateral eye, many principles underlying the functioning of all visual systems were discovered and gave Dr H. Keffer Hartline a shared part of the 1967 Nobel Prize.

25. Horseshoe Crabs also have a very important use for humans.  The medical profession uses an extract from the Crabs blue, copper-based blood , called lysate, to test the purity of medicines. Certain  properties of the shell have also been used to speed blood clotting and to make absorbable sutures. Horseshoe Crabs have also bee to benefit cancer research. Pharmaceutical companies extract up to one-third of the animals blood volume and the animal is returned safely to the water and bled animals have a 90% survival rate.

26. Horseshoe crabs have been important in various medical studies for surgical sutures, bacteria detection, wound dressing development and even ophthalmology.

27. Worth only one to two dollars as bait for eels and conch in the United States, pre-cooked female horseshoe crabs are a delicacy in China and sell for $200-400 HK ($25-50 US) in Hong Kong seafood shops. Street market prices are slightly lower, between $45-100 HK ($6-13 US).

28. They can swim upside down.

29. Their eggs are an essential food source for many migrating shorebirds, including red knots, semipalmated sandpipers, sanderlings and dowitchers; and their eggs and larvae are consumed by many fish, such as American eel, killifish, weakfish, silversides, summer flounder and winter flounder.


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