The Horse Shoe Crab: Interesting Arthropod for a Species Tank

If you have ever taken a walk along the edge of the beach and see something resembling a Volkswagen Bug with eight legs and Bulging eyes with a turtle tail, you have a horse shoe crab. I guess you could even say that it looks much like a shield used by the knights back in Medieval days of old. At any rate the fact that the Horseshoe crab can be traced back some 445 million years to the Ordovician Period means that their ability to evolve and adapt has been very effective as their are no kinks in their armor.

Horseshoe crabs are common from the Gulf of Mexico north along the Atlantic Coast of North America. Their are two species of horseshoe crab that are endemic to India and one species endemic to Japan. Other than that they are confined to North America with the possible exception of stray horseshoe crabs that find their way on to European shores.

A horseshoe crab is basically broken down into three parts: the carapace or head which is the smooth part of the crab includes five pairs of eyes, a pair of pinchers and five pairs of legs and a mouth. The second part is its abdomen or middle where the gills and genitals are located. the last part is its tail section also known as a telson. This tail part is very important to a horseshoe crab because it enables the crab to right itself if it gets flipped upside down through predation falling or water current.

One piece of interesting news regarding the horseshoe crab is the fact that their main migration travels lands them in the Delaware Bay each year for breeding purposes. I have personally seen horseshoe crabs breeding ritual here on the coast of Connecticut. Mating is portrayed as a piggy back affair, where the smaller male grabs hold of the female and attaches itself to the back of her shell with its front claws, holding on for up to a month or so. Once the female has deposited her eggs in a sand nest, the male is responsible for fertilizing the eggs with his sperm. Baby horseshoe will reach maturity at around 9 years and live for a period of 25 years or so. Growth of the horseshoe is provided by their ability to molt. Similar to crabs, lizards and snakes the process of molting is a result of the animals growing in size and when this happens the animal slips out of its existing shell, or in the case of snakes and lizards, its skin which no longer fits. This process would be like us replacing a pair of shoes or pants as we grow from infancy to adulthood.

A very unique ability for horseshoe crabs to regenerate a part of their body should it be lost as a result of predation or environmental conditions, is a process that is shared with Sea Stars.

Horseshoe crabs are opportunistic feeders that rely on mollusks, annelid worms and other benthic crustaceans for their food requirements. Lacking jaws and teeth, the horseshoe crab uses its hairy legs to help break down its food to smaller more digestible particles. They also have a gizzard that is filled with sand and gravel that allows them to grind up their food, a process that is very similar to that found in birds.

If there is anyone out there that wishes to add a horseshoe crab to their bioload because the crab is interesting, diverse or cute, their are some concerns that need to be addressed. Horseshoe crabs can grow to large proportions(up to 24 inches in length), making them not very suitable to those maintaining small aquariums. They are like small bulldozers and this fact makes them unsuitable as ideal reef aquarium mates, for fear that they will knock over corals and live rock causing any number of potential disasters. They will not feed upon corals though as mentioned above sessile benthic invertebrates can be fair game in their book. Now, if you have a fish only aquarium and would like to add one of these animals, that would be fine, again having a large aquarium with ample space(sandy bottom) for them to effectively get around and forage for food will work. The horseshoe crab isn't what you would call a mainstay in the marine aquarium hobby, but that is what entices many aquarists to experiment with one of these arthropods. Much like a jellyfish, sting ray, Octopus, Mantis shrimp or small species of shark, there are aquarists out there with a desire for the unknown and unique animal to be part of their marine habitat.

The same issues must be ascertained when deciding on purchasing a horseshoe crab for your aquarium as other inverts, fish and corals. Maintaining ideal water parameters with limiting the possibility of having a spike or lull in the water's chemistry at all costs. Making sure that the crab has sufficient food is also important, which may include target feeding your crab to ensure that it is eating.

The horseshoe crab has been an important animal in the past few years, not to the aquarium hobby but to the medical profession. Extensive studies and tests have been performed using the blood on the horseshoe crab to detect bacterial endotoxins, blood clotting possibilities and as a remedy for those diseases that are resistant to penicillin. The unique thing regarding the blood of the horseshoe crab is that the color of its blood is pale yellow to grayish white. Horseshoe crabs along with gastropods, many other mollusks and cephalopods do not possess hemoglobin(iron containing protein) that is responsible for transporting oxygen rich blood (red blood cells)to all intracellular areas of vertebrates. Instead, these animals contain a copper based protein known as hemocyanin that acts like our hemoglobin but carries oxygen in extracellular fluids. Although this protein is colorless under reduced or oxygen depleted blood, when exposed to oxygen such as when it bleeds, the blood turns a beep blue color. The blood of the horseshoe crab contains just one type of blood cell which is known as amebocytes, and it is because of this that many beneficial medical advances have been discovered in recent years. Test have been ongoing as coagulation(blood clotting) and pathogen and bacterial defensive measures are improved upon and better understood.

Conservative efforts have been instilled as of late due to various factors that are reducing the horseshoe crabs numbers in recent years. Over harvesting, environmental issues, such as pollution, and predatory birds, such as the Red Knot and other shore birds are also responsible for their dwindling numbers by feeding on the eggs layed by the horseshoe crabs. A non-profit group known as the Ecological and Research Development Group(ERDG) and the Atlantic States Marine Fisheries Commission have become prominent aids in helping the horseshoe crab from ending up on the endangered list through ordinances and other conservative options. With their conscientious efforts and our awareness, appreciation and understanding of these unique and important animals, we can ensure that this arthropod will be able to thrive and reproduce for years to come. Whether you are planning on purchasing one of these for your aquarium or admiration while viewing these animals in their natural habitat, they are truly an interesting animal that deserves our attention and protective efforts as well.

http://en.wikipedia.org/wiki/Horseshoe_crab