A relict species whose roots date back to the middle Silurian EraThese very distinctive animals were once much more widespread on earth. They belong to order Xiphosura , of which four species have survived to the present day. The most common of these is actually the Horseshoe crab, which is found in Atlantic and Pacific waters. These animals are used in fisheries and in the biomedical industry. They are also an important part of the Delaware Bay ecosystem, where the eggs they lay are one of the staple foods in the diets of the bay's resident birds.
1.Despite their appearance, they are more related to spiders, ticks and scorpions than to crabs.
2.Limulus is a genus of horseshoe crab, with one extant species, the Atlantic horseshoe crab (Limulus polyphemus). Limulus first appeared on earth about 425 million years ago during the Silurian period.
3.They live in the Atlantic Ocean near the coast of North and Central America and near the Asian coasts in the Pacific.
4.Limulus living today are saltwater animals. Fossil specimens also inhabited freshwater enviroments.
Currently living horseshoe crabs evolved 244 million years ago and are now considered living fossils as they didn't change a lot since then.
5.The chitinous armor of the horseshoe crabs is bisected, similar to that of scorpions.
It consists of an anterior part or prosoma and a posterior part or opisthosoma. Prosoma of horseshoe crabs consists of 6-7 segments, while opisthosoma consists of 10 segments. The posterior-most division of the body of animal is called telson which is a long spike.
6.They swim mostly upside down.
When swimming, they tilt at an angle of about 30° to the horizontal plane and move at a speed of about 10-15 cm/s.
7.The horseshoe tail spike helps them swim and acts as a rudder. It is also helpful in burying the animal.
8.Horseshoe crab can grow up to 60 cm in length.
Females are approximately 20% - 30% larger than males.
9.An adult animal weighs up to 4.5 kilograms.
10.During the breeding season, horseshoe crabs migrate to shallow coastal waters.
The smaller male clings to the back of the larger female with specialized front claws and fertilizes the eggs, which are then deposited in the sand.