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More About Horseshoe Crabs ...
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The horseshoe crab, Limulus polyphemus, is an arthropod that is more closely related to spiders than crabs. They are most commonly found in the Gulf of Mexico and along the Northern Atlantic coast. They can grow up to 51 cm, on a diet of mollusks, worms, and other invertebrates, which they find under the sand where they spend most of their lives. In captivity, its diet should be supplemented with meaty items such as pieces of squid and shrimp. (Foster and Smith, 2004) Its mouth is located in the middle of the underside of the cephalothorax. A pair of pincers (chelicerae) for seizing food are found on each side of the mouth.
Horseshoe crabs have gills located just behind their appendages that allow them to breathe underwater. The outer shell of these animals consists of three parts. The carapace is the smooth frontmost part of the crab; it has on it the eyes, the walking legs, the chelicera (pincers), the mouth, the brain, and the heart. The abdomen is the middle portion where the gills are attached as well as the genital operculum. The last section is the telson which is used to flip itself over if stuck upside down.
Limulus has been extensively used in research into the physiology of vision. It has a compound eye, and each ommatidium feeds into a single nerve fibre. Furthermore the nerves are large and relatively accessible. This made it possible for electrophysiologists to record the nervous response to light stimulation easily, and to observe visual phenomena like lateral inhibition working at the cellular level. More recently, behavioural experiments have investigated the functions of visual perception in Limulus. Habituation and classical conditioning to light stimuli have been demonstrated, as has the use of brightness and shape information by male Limuli when recognising potential mates.
Since 1964 a substance in their blood called Limulus amebocyte lysate (LAL) has also been used to test for bacterial endotoxins in pharmaceuticals and for several bacterial diseases. The animals can be returned to water after extraction of a portion of their blood (except in Massachusetts), so this is not necessarily a threat to the survival of horseshoe crabs.
Horseshoe crabs can live for sixteen to seventeen years. They migrate into the shore in late spring, with the male arriving first. The female then arrives and makes a nest at a depth of 15-20cm in the sand. In the nest, females deposit eggs which are subsequently fertilized by the male. Studies conducted in Delaware have revealed an average of 3,650 eggs laid per nest. ?Development begins when the first egg cover split and new membrane, secreted by the embryo, forms a transparent spherical capsule? (Sturtevant). The larvae form and these larvae swim for about five to seven days. After swimming they settle, and begin the first molt: this happens approximately twenty days after the formation of the egg capsule. As young horseshoe crabs grow, they move to deeper waters. During this time, molting still takes place for two to three years. They reach sexual maturity in five to seven years. The main cause of death during these days is the fish bait industry, which collects horseshoe crabs to make bait for lobsters and other catches.
Some arthropods have mandibles, however the horseshoe crab is jawless.
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Source: Wikipedia Read more about Horseshoe Crabs
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VIDEO CLIPS
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Horseshoe Crab
Streaming RAM View Movie
Discovery.com
Living Fossils
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Horseshoe Crab
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baylink.org
Horseshoe Crab video clip
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Horseshoe Crab
0.460MB MOV View Movie
baylink.org
Horseshoe Crab video clip
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