Agriculture
Microbes at the Gas Pump
Earth-Friendly Fabrics
Treating peanut allergy bit by bit
Amphibians
Toads
Newts
Tree Frogs
Animals
Firefly Delight
Jay Watch
A Tongue and a Half
Behavior
When Darwin got sick of feathers
Sugar-pill medicine
Brainy bees know two from three
Birds
Nightingales
A Meal Plan for Birds
Pheasants
Chemistry and Materials
Pencil Thin
Makeup Science
A Framework for Growing Bone
Computers
Two monkeys see a more colorful world
Toxic Dirt + Avian Flu = Science Fair Success
Secrets of an Ancient Computer
Dinosaurs and Fossils
South America's sticky tar pits
Mammals in the Shadow of Dinosaurs
Ancient Critter Caught Shedding Its Skin
E Learning Jamaica
E Learning in Jamaica WIN PRIZES and try our Fun Animated Games
Results of GSAT are in schools this week
2014 GSAT Results for Jamaican Kids
Earth
Watering the Air
Ancient Heights
Science loses out when ice caps melt
Environment
Fishing for Fun Takes Toll
Eating Up Foul Sewage Smells
Snow Traps
Finding the Past
Settling the Americas
Ancient Cave Behavior
Ancient Art on the Rocks
Fish
Eels
Pygmy Sharks
Swordfish
Food and Nutrition
A Taste for Cheese
In Search of the Perfect French Fry
A Pepper Part that Burns Fat
GSAT English Rules
Who vs. That vs. Which
Adjectives and Adverbs
Who vs. Whom
GSAT Exam Preparation Jamaica
2014 GSAT Results for Jamaican Kids
Tarrant High overcoming the odds
March 21-22, 2013: Over 43,000 students will take the GSAT Exam
GSAT Exams Jamaica Scholarships
GSAT stars reap scholarship glory
GSAT Exam Preparation
GSAT Scholarship
GSAT Mathematics
E Learning in Jamaica WIN PRIZES and try our Fun Animated Games
Math is a real brain bender
Math and our number sense: PassGSAT.com
Human Body
A Sour Taste in Your Mouth
Workouts: Does Stretching Help?
Smiles Turn Away Colds
Invertebrates
Horseshoe Crabs
Roundworms
Worms
Mammals
Pomeranians
Miniature Schnauzers
Rats
Parents
Children and Media
What Not to Say to Emerging Readers
Raise a Lifelong Reader by Reading Aloud
Physics
Dreams of Floating in Space
Powering Ball Lightning
The Particle Zoo
Plants
Assembling the Tree of Life
Fastest Plant on Earth
Farms sprout in cities
Reptiles
Black Mamba
Crocodiles
Rattlesnakes
Space and Astronomy
Planet Hunters Nab Three More
Supernovas Shed Light on Dark Energy
Ready, Set, Supernova
Technology and Engineering
Space Umbrellas to Shield Earth
Riding Sunlight
A Micro-Dose of Your Own Medicine
The Parts of Speech
Adjectives and Adverbs
Countable and Uncountable Nouns
What is a Noun
Transportation
Robots on the Road, Again
Tinkering With the Basic Bike
Robots on a Rocky Road
Weather
Watering the Air
A Dire Shortage of Water
Warmest Year on Record
Add your Article

Horseshoe Crabs

The horseshoe crab (Limulus polyphemus) is a chelicerate arthropod, therefore it is more closely related to spiders and scorpions than crabs. They are most commonly found in the Gulf of Mexico and along the northern Atlantic coast of North America. A main area of annual migration is the Delaware Bay. Size: They can grow up to 20 inches (51 cm), on a diet of mollusks, annelid worms, and other benthic invertebrates. 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. Book gills: Horseshoe crabs possess five pairs of book gills located just behind their appendages that allow them to breathe underwater, and can also allow them to breathe on land for short periods of time, provided the lungs remain moist. Outer Shell: The outer shell of these animals consists of three parts. The carapace is the smooth frontmost part of the crab which contains 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" (caudal spine) which is used to flip itself over if stuck upside down. Eyes: The horseshoe crab has been extensively used in research into the physiology of vision. It has four compound eyes, 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, behavioral 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 recognizing potential mates. Among other senses, they have a small sense organ on the triangular area formed by the exoskeleton beneath the body near the ventral eyes. Mandibles: Although most arthropods have mandibles, the horseshoe crab is jawless. The horseshoe crab's mouth is located in the center of the body. In the female, the four large legs are all alike, and end in pincers. In the male, the first of the four large legs is modified, with a bulbuous claw that serves to lock the male to the female while she deposits the eggs and he waits to fertilize them. Their body also contains a cartilaginous tissue. Regeneration: Horseshoe crabs possess the rare ability to regrow limbs lost, in a manner similar to sea stars. This attribute was recently proven by Sue Shaller of the United States Fish and Wildlife Service. Medical research: Horseshoe crabs are extremely valuable as a species to the medical research community. Since 1964 a substance made from 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, so this is not necessarily a threat to the survival of horseshoe crabs. A single horseshoe crab can be worth $2,500 over its lifetime for periodically drawing its blood for this extract. Blue blood: The blood of horseshoe crabs is blue, which is a result of its high content in copper-based hemocyanin instead of the iron-based hemoglobin found, for example, in humans. The fact that horseshoe crabs have evolved so little over the past 300 to 400 million years is part of the reason why they are so different from most other animals. Conservation: 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. In 1995, the nonprofit Ecological Research and Development Group (ERDG) was founded with the aim of preserving the four remaining species of horseshoe crab. Since its inception, the ERDG has made significant contributions to horseshoe crab conservation. ERDG founder Glenn Gauvry designed a mesh bag for conch traps, to prevent other species from taking off with the bait. This has led to the amount of bait needed being decreased by approximately 50%. In the state of Virginia, these mesh bags are now mandatory in conch fishery. The Atlantic States Marine Fisheries Commission is in 2006 considering several conservation options, among them being a two-year ban on harvesting the animals affecting both Delaware and New Jersey shores of Delaware Bay. 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. Conservationists have also voiced concerns about the declining population of shorebirds, such as Red Knots, which rely heavily on the horseshoe crabs' eggs for food during their Spring migration. Precipitous declines in the population of the Red Knots have been observed in recent years. Predators of horseshoe crabs, such as the currently threatened Atlantic Loggerhead Turtle, have also suffered as crab populations diminish. Horseshoe crabs can live for 20-25 years. They migrate into the shore in late spring, with the males arriving first. The females then arrive and make nests at a depth of 15-20 cm in the sand. In the nests, females deposit eggs which are subsequently fertilized by the male. Egg quantity is dependent on female body size and ranges from 15,000-64,000 eggs per female (Leschen et al. 2006). "Development begins when the first egg cover splits and new membrane, secreted by the embryo, forms a transparent spherical capsule" (Sturtevant). The larvae form and then swim for about five to seven days. After swimming they settle, and begin the first molt. This occurs approximately twenty days after the formation of the egg capsule. As young horseshoe crabs grow, they move to deeper waters, where molting continues. They reach sexual maturity in approximately eleven years and may live another 10-14 years beyond that. Horseshoe crabs are distant relatives of spiders and are probably descended from the ancient eurypterids (sea scorpions). They evolved in the shallow seas of the Paleozoic Era (540-248 million years ago) with other primitive arthropods like the trilobites. Horseshoe crabs are one of the oldest classes of marine arthropods, and are often referred to as "living fossils", as they have not changed much in the last 350 to 400 million years.

Horseshoe Crabs
Horseshoe Crabs








Designed and Powered by HBJamaica.com™