The horseshoe crab looks a bit like a creature from another planet, but it is a living fossil. The animal resembles a crab or lobster with its exoskeleton, but descends from a group of arachnids. The horseshoe crab is not only special because of its appearance or because it has been living for so long, but also because the animal can help mankind and especially the medical world.
The history
Although the horseshoe crab sounds like a crab and looks a bit like a lobster, the horseshoe crab belongs to the group of spiders. The group was called Xiphosuridae, but the horseshoe crab is now a living fossil. That means that the rest of the animals that belonged to the group Xiphosuridae are extinct. The youngest fossil remains of that group found are 50 million years old. The oldest fossil remains of a horseshoe crab are more than 350 million years old. The dinosaurs didn’t appear until 100 million years later. Miraculously, the horseshoe crab has managed to survive all this time, in fact the horseshoe crab does not seem to have changed anything in terms of appearance.
The habitat and reproduction
The horseshoe crab mainly lives in water and only comes ashore to reproduce. They live on the south-east coast of America. During the mating season, Delaware Bay beach is almost invisible due to the number of horseshoe crabs that reproduce simultaneously. A female lays about 4000 eggs in the sand. The eggs are laid in such a way that they are under water at high tide and surface at low tide. The eggs that get the most heat seem to hatch the fastest. Usually the eggs hatch around 14 days. The horseshoe crab then goes a little deeper into the water, but stays on the bottom just below the water’s surface to eat. The horseshoe crab mainly feeds on worms and mussels. They spend about two years there before they actually go into the deep water.
The appearance
The body
From the top you can see a roundish armor which is divided into two parts. The abdomen is, as it were, attached with a hinge to the front, which consists of the thorax and the head. When in an animal the head and chest piece are together, this is also called the cephalothorax. From the top you can also see the tail of the horseshoe crab which it can use to turn itself over if it lands on its head. From head to tail, the horseshoe crab is on average around 60 cm.
If you turn the horseshoe crab you will see that it has 10 legs, on 8 of the legs you will see a kind of scissors at the end which we also see in lobsters. The end of the two rear legs almost looks like a flower, these are really meant to be put off. In a male, the front legs have a kind of hooks to hold the female during reproduction. To eat its prey, the horseshoe crab has chelicerae, these are mouth parts, as it were, which resemble tongs with which the horseshoe crab can hold food. His mouth is in the middle of his legs, he has no jaws but palps which are a kind of spines on the side of the mouth to force the food in.
The eyes
The horseshoe crab has multiple eyes, although not all eyes can see.
- The Parietal eye which occurs in more reptiles ensures the production of hormones and the regulation of the temperature. The eye sees can only distinguish dark and light, but sees nothing else.
- The Median eye helps navigate using the sunlight.
- The Vental eyes which help orient him while swimming.
- The Compound eyes which are made up of all small particles, as we see in the Libelle. Compound eyes can adapt to the light. This allows the horseshoe crab to find prey or mate in the dark.
- The horseshoe crab’s state also contains light receptors that allow the horseshoe crab to receive signals in the brain that it is light or dark.
Useful to humanity
The horseshoe crab is not often seen, but since they can be found en masse at the same time on the beach, the horseshoe crabs can easily be caught during the mating season. The Indians already used the animals for food and their shield as shovels in the canoe to scoop the water out. The horseshoe crab was also ground up and used for land. It turned out to be a good fertilizer because it contains a lot of nitrogen which is slowly released into the soil. The manure was so popular that the number of horseshoe crabs started to decline, as it became more difficult to catch the animals and a cheaper fertilizer was developed, the horseshoe crab was able to return in numbers.
Shield against blood
The shell of the horseshoe crab contains chitin, a material that provides strength. The chitin mixed with a chemical agent forms Citosan. Chitosan has a positive electrical charge that attracts negatively charged red blood cells. The chitosan then forms a clot with the blood cells that stops the bleeding. Cardiologist Kenton Gergory developed a link with chitosan. The bacteria also stick to the dressing, which means that the dressing prevents bleeding and also has an antibacterial effect. It is now widely used by medical personnel.
Blue blood
The horseshoe crab’s blood is literally blue blood. The blue blood contains amoebocytes and protects the horseshoe crab against viruses and bacteria. This helps to clarify how the horseshoe crab has managed to survive all this time. Doctor and researcher Frederik Bang injected the horseshoe crab with bacteria and saw that the blood formed clumps of gel. The horseshoe crab is therefore able to eliminate toxins. They can now test injectable drugs for toxins from bacteria. If patients ingest this, the patient can die from it. Previously, tests were therefore first carried out with rabbits, but thanks to the horseshoe crab that is no longer necessary. The gel-forming proteins are taken from the blood and they add this to test a drug. If a clot forms, the drug is not suitable for use. Now blood is taken from the horseshoe crabs in a laboratory, after which it is released again. After a few months his blood is back to normal.
The horseshoe crab as bait
The horseshoe crabs that come into the laboratory are lucky to be released again. The horseshoe crab has few natural enemies, but humans are a threat. The female horseshoe crab contains a protein that attracts eels. So they are put in an eel cage by fishermen as bait to catch eels.