Is Limulus an Arachnid?A. S. Packard, Jr.The American Naturalist, Vol. 16, No. 4. (Apr., 1882), pp. 287-292.
HORSESHOE CRABS Some Facts Horseshoe crabs, common along the Delaware coast, are estimated to be at least 300 million years old. They have survived because of their hard, curved shells, which have made it difficult for predators to overturn them and expose their soft, vulnerable underbellies. The horseshoe crab has also survived because it can go a year without eating and endure extreme temperatures and salinity.without eating and endure extreme temperatures and salinity. Called "Horsefoot Crabs" because of the resemblance of its shell to a horse hoof. The Horseshoe Crab isn't really a crab. It is related to scorpions, ticks and land spiders, horseshoe crabs have their own classification (Class Merostomata).
Photo: University of Delaware www.ocean.udel.edu
Life Stages From Egg to Trilobite Larva After fertilization, the eggs begin to develop into trilobite larvae. By day five, miniature legs are visible inside the translucent egg. Upon hatching, the trilobite larvae dig their way out of the sand.They are approximately 3 mm (1/8 inch) across and look just like miniature adults, but lack a movable tail and functional compound eyes. Their digestive system is also not yet functional, and the baby crabs swim around for about a week absorbing the yolk sac as their digestive systems mature. It Takes Eight to Ten Years for Horseshoe Crabs to Reach Adulthood!
Living Fossils Most scientists believe that horseshoe crabs are the closest living relative of the trilobite, a marine animal that has long been extinct. Scientists believe that horseshoe crabs were among the dominant creatures some 300 million years ago.
Name: Paleomerus hamiltoni (cast) Locality: Kinnekulle, Sweden Age: Early Cambrian Showcase: Chelicerata showcase The oldest known Horseshoe Crab. Other chelicerata in the exhibition
Human UseFarmers in the years 1800 - 1920 used horseshoe crabs for fertilizer Some farmers also used horseshoe crabs as a cheap source of food for chickens and hogs. However, the crabs gave the meat a "fishy" taste that required weeks of purging on grain to remove.
Dr. Bang and Dr. Levin had created Limulus amoebocyte lysate, or LAL, and a new method to test for gram-negative bacteria. It was so effective that the U.S. Food and Drug Administration (FDA) accepted it as a standard test for endotoxins in 1983. Since then, LAL has gained widespread use, replacing rabbit tests for clinical and biomedical applications
The CritiqueOf these days
HORSESHOE CRABS TodayLimulus polyphemus is not presently endangered, but harvesting and habitat destruction have reduced its numbers at some locations and caused some concern for these animals' future. Since the 1970s, the horseshoe crab population has been decreasing in some areas, owing to several factors, including the use of the crab as bait in conch trapping. In 1995, the nonprofit Ecological Research and Development Group (ERDG) was founded with the aim of preserving the four remaining species of horseshoe crab. Every year, around 10% of the horseshoe crab's breeding population dies when rough surf flips the creatures onto their backs, a position from which they often cannot right themselves. In response, the ERDG (Ecological Resource and Development Group) launched a "Just Flip 'Em" campaign, in the hopes that beachgoers will simply turn the crabs back over.
Originally thought to be crustaceans(hence the common name), xiphosurans were recognizedas aquatic chelicerates late in the 19th century(Lankester 1881). The fossil record of horseshoe crabsgoes back to the Devonian, and modern-looking horseshoecrabs first appear in the mid-Mesozoic (Strmer1952). Their apparently slow rate of morphologicalchange since has led to their being dubbed living fossils(Fisher 1984) and regarded as a keystone groupfor studies of evolution and of arthropod phylogeny.(The Complete Mitochondrial DNA Sequence of the Horseshoe Crab Limulus polyphemus)
The earliest horseshoe crab species were crawling around the Earth's shallow coastal seas for at least 100 million years before the dinosaurs even arrived (which was about 200 million years ago). A great similarity to a studentHorseshoe crabs can live for 20-25 years. the oldest known horseshoe crab fossil at the University of Oslo's Paleontology museum. Medical Application: Early on it was found that chitin had wound-healing properties. By the mid-1950s, chitin-coated sutures were being used, which enhanced healing time by 35 to 50%. Horseshoe crabs are extremely valuable as a species to the medical research community. The horseshoe crab has a simple, but amazing immune system. When a foreign object (bacteria) enters through a wound in their body, it almost immediately clots into a clear, gel like material, thus effectively trapping the bacteria. This substance in called Limulus Amebocyte Lysate (LAL) and is being used to test for bacterial endotoxins in pharmaceuticals and for several bacterial diseases. If the bacteria is harmful, the blood will form a clot. Horseshoe crabs are proving to be very helpful in finding remedies for diseases that have built an immunity against penicillin and other drugs. Cartenoid Pigments in the coxal gland of Limulus.pdf
Cartenoid Pigments in the coxal gland of Limulus.pdfNear Threatened (NT or LR/nt), is close to qualifying for or is likely to qualify for a threatened category in the near future.
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