Horseshoe crabs are a very old species and are frequently called “living fossils.” Their earliest known fossil ancestors date to the Ordovician Period (485.4 to 443.8 million years ago), and horseshoe crab-like creatures originated in the Jurassic Period (201.3 to 145 million years ago). On the east coastlines of Asia and North America, there are four species of marine arthropods known collectively as horseshoe crabs. Although they go by the term “crabs,” these creatures are actually linked to scorpions, spiders, and extinct trilobites.
The cephalothorax, which is large and shaped like a horseshoe, the abdomen, which is much smaller and segmented, and the telson, which is a long, sharp tail-spine, are all portions of the horseshoe crab’s body that are hinged together. A pair of lateral compound eyes and a much smaller median pair of UV-responsive eyes are located on the cephalothorax’s smoothly arched top surface.
The commercial fishing industry collects American horseshoe crabs to use as bait to catch American eels, which are then used as bait for striped bass and whelks. Additionally, the American horseshoe crab has been used in the biomedical business since the 1960s because the species’ blood includes coagulogen, a very basic clotting factor.
American haematologist Jack Levin created the Limulus amoebocyte lysate (LAL) test for the presence of gram-negative bacteria in injections in the 1960s as a result of American scientist Frederick Bang’s 1956 discovery of coagulogen.
The American horseshoe crab was listed as a vulnerable species by the International Union for Conservation of Nature in 2016 and the Japanese horseshoe crab as an endangered species in 2018. Data for the other two species of horseshoe crabs, however, are still lacking.
