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Is Limulus an Arachnid? A. S. Packard, Jr. The American Naturalist, Vol. 16, No. 4. (Apr., 1882), pp. 287-292.

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Presentation on theme: "Is Limulus an Arachnid? A. S. Packard, Jr. The American Naturalist, Vol. 16, No. 4. (Apr., 1882), pp. 287-292."— Presentation transcript:

1 Is Limulus an Arachnid? A. S. Packard, Jr. The American Naturalist, Vol. 16, No. 4. (Apr., 1882), pp

2 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. Photo: Univer sity of Delaw are cean.u del.ed u cean.u del.ed u 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).

3 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!

4 Name: Paleomerus hamiltoni (cast) Locality: Kinnekulle, Sweden Age: Early Cambrian Early Cambrian Showcase: Chelicerata showcase Chelicerata showcase The oldest known Horseshoe Crab. Other chelicerata in the exhibition chelicerata in the exhibition 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.

5 Human Use Farmers in the years 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.

6 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 Since then, LAL has gained widespread use, replacing rabbit tests for clinical and biomedical applications

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9 The Critique Of these days

10 HORSESHOE CRABS Today Limulus 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.endangeredhabitat destructionconch In 1995, the nonprofit Ecological Research and Development Group (ERDG) was founded with the aim of preserving the four remaining species of horseshoe crab.Ecological Research and Development Group Just Flip 'Em 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.

11 Originally thought to be crustaceans (hence the common name), xiphosurans were recognized as aquatic chelicerates late in the 19th century (Lankester 1881). The fossil record of horseshoe crabs goes back to the Devonian, and modern-looking horseshoe crabs first appear in the mid-Mesozoic (Størmer 1952). Their apparently slow rate of morphological change since has led to their being dubbed ‘‘living fossils’’ (Fisher 1984) and regarded as a keystone group for studies of evolution and of arthropod phylogeny. (The Complete Mitochondrial DNA Sequence of the Horseshoe Crab Limulus polyphemus)


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