Agriculture
Springing forward
Where Have All the Bees Gone?
Earth-Friendly Fabrics
Amphibians
Frogs and Toads
Poison Dart Frogs
Tree Frogs
Animals
Killer Flatworms Hunt with Poison
Mating Slows Down Prairie Dogs
Navigating by the Light of the Moon
Behavior
The Other Side of the Zoo Fence
Pain Expectations
Mice sense each other's fear
Birds
Cardinals
Songbirds
Turkeys
Chemistry and Materials
Big Machine Reveals Small Worlds
The Incredible Shrunken Kids
The chemistry of sleeplessness
Computers
Electronic Paper Turns a Page
The hungry blob at the edge of the universe
The Shape of the Internet
Dinosaurs and Fossils
Tiny Pterodactyl
Dino Flesh from Fossil Bone
A Dino King's Ancestor
E Learning Jamaica
E Learning in Jamaica WIN PRIZES and try our Fun Animated Games
2014 GSAT Results for Jamaican Kids
Results of GSAT are in schools this week
Earth
Less Mixing Can Affect Lake's Ecosystem
Quick Quake Alerts
Rodent Rubbish as an Ice-Age Thermometer
Environment
Pumping Up Poison Ivy
Indoor ozone stopper
Nanosponges Soak Up Pollutants
Finding the Past
Early Maya Writing
A Human Migration Fueled by Dung?
Words of the Distant Past
Fish
Halibut
Puffer Fish
Great White Shark
Food and Nutrition
Packing Fat
Symbols from the Stone Age
Moving Good Fats from Fish to Mice
GSAT English Rules
Who vs. Whom
Who vs. That vs. Which
Finding Subjects and Verbs
GSAT Exam Preparation Jamaica
Results of GSAT are in schools this week
Ministry of Education Announces 82 GSAT Scholarships for 2010
GSAT Practice Papers | GSAT Mathematics | Maths
GSAT Exams Jamaica Scholarships
Results of GSAT are in schools this week
2014 GSAT Results for Jamaican Kids
42,000 students will sit for the GSAT Exam in two weeks
GSAT Mathematics
Setting a Prime Number Record
Losing with Heads or Tails
How to Slice a Cake Fairly
Human Body
Sleeping Soundly for a Longer Life
Heart Revival
Heavy Sleep
Invertebrates
Moths
Walking Sticks
Millipedes
Mammals
Primates
Gazelle
Bumblebee Bats
Parents
Raise a Lifelong Reader by Reading Aloud
Choosing a Preschool: What to Consider
Expert report highlights the importance to parents of reading to children!
Physics
Dreams of Floating in Space
Echoes of a Stretched Egg
IceCube Science
Plants
Surprise Visitor
Getting the dirt on carbon
Pumping Up Poison Ivy
Reptiles
Snakes
Lizards
Turtles
Space and Astronomy
Intruder Alert: Sweeping Space for Dust
Sounds of Titan
Cousin Earth
Technology and Engineering
Smart Windows
A Satellite of Your Own
Shape Shifting
The Parts of Speech
Problems with Prepositions
Adjectives and Adverbs
What is a Preposition?
Transportation
Morphing a Wing to Save Fuel
Troubles with Hubble
Seen on the Science Fair Scene
Weather
Earth's Poles in Peril
Where rivers run uphill
Watering the Air
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™