Today, we use horseshoe crabs quite differently. Scientists have learned a lot about how our eyes work by conducting research on the horseshoe crab s large, compound eyes. (Can you locate these two eyes on your model?) Chitin (kī -tin), the substance that makes up the horseshoe crab s shell, is used in surgical sutures and bandages that promote healing. Also, without a chemical known as lysate (lī -sāt) obtained from the horseshoe crab s blood cells, the diagnosis of certain diseases like spinal meningitis would take a lot longer, and we might be exposed to bacterial contamination in the prescription drugs we take. Fortunately, we can collect the lysate without harming the animals. In the Delaware Bay area, people get together each spring to count the horseshoe crabs that appear on the beach to spawn so that we can keep track of their population. A few states have even passed laws to protect them. It would be sad, indeed, if a creature as hardy and as valuable as the horseshoe crab were someday wiped out by human interference. For Further Exploration Bergson, J., and C. Shuster, Jr. 1999. The Horseshoe Crab: Battle for a True Multiple-Use Fishery. Fisheries 24 (11): 6 10. Delaware Sea Grant and Mid-Atlantic Sea Grant Network. 2004. Horseshoe Crab. http://www.ocean.udel.edu/ horseshoecrab/ Dunlap, J. 1999. Extraordinary Horseshoe Crabs. (For grades 2 5.) Minneapolis: Lerner. Ecological Research and Development Group. 2003. The Horseshoe Crab. http://horseshoecrab.org/ *Hall, W. R. 2006 (revised). The Horseshoe Crab: A Creature That Crawled Out of the Past. Newark, DE: Delaware Sea Grant College Program. Maryland Dept. of Natural Resources. 1995 2005. Horseshoe Crabs: A Living Fossil. http://www.dnr.state. md.us/education/horseshoecrab/ Sekiguchi, K. 1988. The Biology of Horseshoe Crabs. Tokyo: Science House. *Editor s Note: The Horseshoe Crab Model is designed as a companion piece to Delaware Sea Grant s educational bulletin, The Horseshoe Crab: A Creature That Crawled Out of the Past. Ordering information for this publication, and others available from Delaware Sea Grant, is below. 10 12 13 15 18 8 20 Across 1. Horseshoe crabs burrow in when the water temperature is low. 3. horseshoe crabs have special hooked claws (pedipalps) that are used during spawning. 4. This substance in horseshoe crab shells is used to make sutures and bandages. 5. is used to diagnose certain diseases such as spinal meningitis. 7. By studying the horseshoe crabʼs large, compound, scientists have learned a lot about our own. 9. Horseshoe crabs live on the Atlantic coast of North America from to the Yucatán. 11. Horseshoe crabs use their book to breathe. 12. Horseshoe crabs donʼt have any of these, which are also known as mandibles. 13. depend on horseshoe crab eggs for food as they fly north to their Arctic nesting grounds. 11 16 Test Your Knowledge! 4 7 17 19 21 1 9 14 2 3 5 6 Check your answers at the bottom of the page! 15. Thousands of horseshoe crabs may be seen spawning on the beaches of Delaware Bay in the late. 16. The horseshoe crabʼs mouth is found on its side. 18. Dead horseshoe crabs were once used as for growing crops. 20. Horseshoe crabs are more closely related to than to crabs. 21. Females lay about 4,000 eggs in a in a sandy beach. Down 2. Horseshoe crabs inhabited the Earth long before the. 3. Horseshoe crabs grow larger by their old shells. 4. Leglike pincers used to push bits of food toward the horseshoe crabʼs mouth. 6. horseshoe crabs are about 11 inches wide. 8. Another name for the horseshoe crabʼs tail. 10. One of the horseshoe crabʼs favorite foods. 14. The largest concentration of horseshoe crabs in the world lives in Bay. 17. A substance in the horseshoe crabʼs cells is used to test drugs for bacteria. 18. The number of horseshoe crab species worldwide. 19. The color of horseshoe crab eggs. 20. Horseshoe crabs live in water. Meeting the Science Standards The Delaware Sea Grant College Program is a member of a national network of universities committed to research, education, and technology transfer designed to meet the changing needs of our ocean, coastal, and Great Lakes regions. The program is funded by the National Oceanic and Atmospheric Administration in the U.S. Dept. of Commerce; the State of Delaware; and the University of Delaware. This publication was produced by Dr. William Hall and Tracey Bryant, writers/editors; David Barczak, art director; Pamela Donnelly, production manager; and the University of Delaware Marine Public Education Office. For more information, contact the UD Marine Public Education Office at 302-831-8083 or MarineCom@udel.edu. For other Delaware Sea Grant publications, visit www.ocean.udel.edu/seagrant. A major goal of science educators is to engage students in activity-based learning. Here are a few examples of how K 12 educators can use the Horseshoe Crab Model to teach the fundamental concepts and principles set forth in the National Science Education Standards: Standard 1. Unifying Concepts & Processes Evolution; organization and taxonomy Standard 2. Science as Inquiry How we know; fossils; eyes; natural history Standard 3. Physical Science Forces and motion in swimming Standard 4. Life Science Anatomical structure and function; reproduction; life cycles Standard 5. Earth & Space Earth s history Standard 6. Science & Technology (Grades 5 8) Products derived from the horseshoe crab, such as Limulus amoebocyte lysate (LAL) and chitin Standard 7. Science in Personal & Social Perspectives Status of world s horseshoe crab population; science, technology, and society Standard 8. History & Nature of Science Medical applications of the horseshoe crab and historical perspectives of the animal s use Crossword Answers: Across 1. mud, 3. male, 4. chitin, 5. lysate, 7. eyes, 9. Maine, 11. gills, 12. jaws, 13. shorebirds, 15. spring, 16. ventral, 18. fertilizer, 20. spiders, 21. nest Crossword Answers: Down 2. dinosaurs, 3. molting, 4. chelicerae, 6. adult, 8. telson, 10. clams, 14. Delaware, 17. blood, 18. four, 19. green, 20. salt 8/2007:5K
3-D MODEL Assembly Time: 15 mins. Fun and educational for all ages! Meets the National Science Education Standards
Horseshoe crabs are among the world s oldest and most fascinating creatures. The earliest horseshoe crab species had already inhabited Earth for at least 100 million years before the dinosaurs arrived about 200 million years ago. Today, there are four species of horseshoe crabs in the world, but only one is found on North American shores. Our native horseshoe crab lives along the Atlantic coast from Maine south to Florida and the Yucatán Peninsula. They are also found several places along the eastern shores of the Gulf of Mexico. But the largest concentration of horseshoe crabs in the world is found in the Delaware Bay, located between Delaware and New Jersey, and the nearby coastal ocean. While it is called a crab, the horseshoe crab actually is more closely related to spiders and scorpions. As you put together your paper model, you ll see that the horseshoe crab has five pairs of claws, but true crabs have only one pair. Also, horseshoe crabs lack antennae and mandibles (jaws) like true crabs have. However, horseshoe crabs do have chelicerae (ke-lis -er-rē) like spiders and scorpions. The chelicerae are the first two small claws located in front of the horseshoe crab s mouth. Horseshoe crabs use their chelicerae as feelers to find food and push it into the mouth. Horseshoe crabs live in salt water on bay or shallow coastal ocean bottoms, searching, digging, and burrowing for food like clams and worms which they identify by both touch and smell. In places where the water stays warm year-round, horseshoe crabs remain active all year. Where water temperatures are low in the winter, they become inactive, burrowing down in the mud to wait for spring. The best time to see live horseshoe crabs is in late spring when they emerge from the water to spawn on bay beaches. The males come ashore first and use two Geographically Speaking Only four species of horseshoe crabs exist today. Three are found in the western Pacific and in the Bay of Bengal. One species, Limulus polyphemus, is found along the western Atlantic coast, from southern Maine to the Yucatán Peninsula. Overharvesting and deterioration of its spawning grounds threaten the horseshoe crab s survival. Japan, for example, once had a thriving population of horseshoe crabs. However, coastal development has made many of Japan s beaches unsuitable for horseshoe crab spawning. Today, there are only about 3,000 horseshoe crabs in Japan, and it is rare to see a single pair of mating horseshoe crabs. In the Delaware Bay, the location of the world s largest horseshoe crab population, you can see horseshoe crabs on almost any spawning beach during the high tides that occur in late spring. However, overharvesting and loss of the horseshoe crab s sandy spawning beaches due to development or beach erosion associated with sea level rise are of increasing concern. Overharvesting is being addressed by state managers through regulation, but the loss of habitat and beach erosion are more difficult to address. The Atlantic Coast horseshoe crab, Limulus polyphemus, is the single most-studied invertebrate animal in the world. Limulus polyphemus Tachypleus tridentatus Tachypleus gigas Carcinoscorplus rotundicanda special pincers called pedipalps (ped -ē-palps), located on their first pair of walking legs, to hook onto a female s abdomen as she heads toward the beach. At the water s edge, the female scoops out a series of five to seven shallow nests in the sand as the tide recedes. She deposits about 4,000 eggs in each nest. The attached male, and other males gathered around the female, fertilize the eggs as she lays them. These pastel-green eggs are an essential source of food for hundreds of thousands of shorebirds on their annual flight north from South America to their Arctic nesting grounds. Young fish also depend on the eggs for food. The surviving eggs may hatch in two weeks to many months later, looking like miniature adults except that their tails are fixed, or non-movable. Over the next 10 years or so, through a process called molting, they will shed their shells, emerging from each molt about 30% larger than before. After about 17 or 18 molts, they reach adult size, which is about 11 inches in width, although females are generally larger than males. The largest one ever seen measured 17 inches wide. Your model represents a horseshoe crab that s five to eight years old. Except for their size, females and males look similar at this age because the males don t gain pedipalps until they are fully grown, at eight or nine years of age. In addition to their important role in the bay ecosystem, horseshoe crabs have been very useful to people over the years. Native Americans ate the meat at the base of the horseshoe crab s tail and possibly some organs and eggs in the prosoma (the helmetshaped part of the shell). They used the shell to bail water from their canoes and the tails as tips for their fishing spears. They also showed the early settlers that dead horseshoe crabs make excellent fertilizer for crops. The horseshoe crabʼs ancestors first appeared on Earth over 100 million years before the dinosaurs.
Top Shell: Dorsal View (Part 1) Build Your Own Horseshoe Crab Front Back Be sure to read this entire publication before assembling your horseshoe crab model. Youʼll need all the information to solve the puzzle on the back page! Did you know that the Native Americans used the horseshoe crabʼs shell to bail water out of their canoes?
Instructions Step 1. Carefully separate the model from the rest of the document by removing the two staples. Step 2. Cut out each part of your model along the solid green lines. The three parts are (1) the top shell, or dorsal view; (2) the bottom shell, or ventral view; and (3) the telson, or tail. Be careful not to cut off the tabs. Mountain Fold Valley Fold Step 3. Create a mountain fold (see diagram at left) along the green dashed line found on the top shell. Create a valley fold (see diagram at left) along the white dashed lines found on the internal side of the top shell. Step 4. Locate the three solid green triangles along the front edge of the top shell. Slide each triangle underneath the shell in the direction indicated by the arrows until the solid green areas Top Shell: Internal (Part 1) Brain Celphalic Artery Cardinal Veins Cardinal Veins Heart Diagram C Step 6. Begin assembly of the tail by mountain folding along the three long and two short green dashed lines. Cover Side A of the tail with Side B, and tape in place. Your tail should now have a tapered, triangular shape that is flat on the bottom and peaked on top (see Diagram C). Next, overlap A with B, covering only the colored area of A to form a semicircular shape, and tape in place. Back Step 7. Align the bottom shell opisthosoma sides to the white dashed lines of the inside of the top shell. Tape just one side in place for now. With the bottom shell facing up, insert the tail s semicircular tab between the top and bottom shells, making sure that the flat, bottom side of the tail also faces up. Now tape the opisthosoma side that was not previously taped. Meet the creature that c
are completely hidden by the shell, and tape in place as you go (see Diagram A). The shell should now have a three-dimensional, helmet-like shape, and the front edge of the shell should form a smooth curve. Diagram A Side View Inside View Step 5. Mountain fold each of the seven tabs along the edges of the bottom shell toward the side with the solid green color. Match the top and bottom shell centers and side edges, with the tabs hidden inside the shell (see Diagram B). Then, starting with one wing and working your way around the front of the shell, tape the edges together on the outside at the tabs. (You don t need to tape the tabs themselves they are there to reinforce the edge of the shell.) Diagram B Bottom Shell Top Shell Telson (Part 3) Front The horseshoe crab was first called the horsefoot crab in 1588 by British naturalist Thomas Hariot. Somehow through time, the name was corrupted to horseshoe. The horseshoe crab s scientific name is Limulus polyphemus. Limulus means a little askew or odd, and polyphemus refers to the giant cyclops of Greek mythology. Despite this frightening comparison, the horseshoe crab is harmless. Bottom Shell (Part 2) Back rawled out of the past!
Bottom B Handle with Care! Despite its threatening appearance, the horseshoe crab is harmless. Its claws aren t sharp. Its long, spike-like tail is NOT poisonous, as some think. The horseshoe crab uses its tail as a lever to right itself when it has been overturned by a wave or a thoughtless person. Sometimes you may see horseshoe crabs standing on their tails on the beach, with their book gills tightly closed to prevent them from drying out. When the next high tide comes, these animals may become afloat again and swim safely back to sea. If you see a stranded horseshoe crab, take special care not to pick it up by its tail, as this could harm the animal. Instead, pick the horseshoe crab up by gripping it under its helmet-like shell, as shown here, and then place it gently in the ocean or bay. Side B Telson (Part 3) Side A A Front Cover Over Light Green Area. Bottom Shell: Ventral View (Part 2) Back How can you tell the difference between a male and a female horseshoe crab? What are some important clues?
A Closer Look at the Horseshoe Crab The body of a horseshoe crab is divided into three parts: the prosoma, opisthosoma, and telson or tail. The prosoma is the large, semicircular part of the horseshoe crab and combines the head and thorax under a hard shell or exoskeleton. It protects the gills and two genital pores. The opisthosoma is attached to the prosoma with a hinge. The top or dorsal surface of the shell has what look like strategically placed ridges and depressions. In actuality, these are locations where muscles are attached to the inside of the shell. Two large compound eyes are located on the prosoma, and eight other simple eyes and light receptors are distributed on the top and bottom of the shell. Under the shell are seven pairs of appendages. Six of the seven pairs have gnathobases, or shoulders of the leg. Five pairs have claws; the first clawed pair are the chelicerae. This pair does not have gnathobases. The second pair of claws, or the pedipalps, are modified on the mature male for grasping the female during reproduction. The sixth pair of appendages are the pusher legs, and the seventh pair are remnant legs called chilaria. A horseshoe crab uses its clawed and pusher appendages to move along the seafloor. It pushes the sediment into little furrows like a farmer plowing a field. The chelicerae act as feelers to determine the presence of prey such as a clam or worm. The horseshoe crab does not have a nose. It smells with tiny hairs on the gnathobases that act as chemoreceptors. When the chelicerae find food, one of the claws will pick it up and push it toward the gnathobases, which are covered with tiny spines or bristles. As the gnathobases move, they grind and crush the food, which gets caught on the bristles. The food is then pushed into the crab s mouth by either the chelicerae, which are in front of the mouth, or the chilaria, which are behind the mouth. Compound Eye Does not function until the animal is 2 3 years old. Simple Lateral Eye Simple Eyes (3) Compound Eye Simple Lateral Eye Ophthalmic Ridge Doublelure Chelicerae Exuviation Suture Flange (for molting) Simple Eyes (2) Chelicerae Pedipalp (see inset below for difference in shape between male and female) Flange Mouth (no jaws) Prosoma Opisthosoma Photoreceptors throughout the length of its tail help set the horseshoe crab s circadian rhythm, or internal clock, to daily cycles of light and darkness. While there are multiple light sensors on the tail, scientists count them as only one eye. Dorsal View Telson (tail) Spines Hinge Celphalic Artery Gnathobases ( shoulders of the leg ) Genital Operculum Male Horseshoe Crab (Limulus polyphemus) Note: This is a mature male, 8 9 years old. Brain Book Gills (five flaps) Telson (tail) Ventral View Anus Pusher Leg Chilaria The pedipalps, or second set of appendages, on the mature male (left) are designed to hook onto the female s shell as she heads to the beach to spawn. Male Female Inside Scoop Before you assemble your horseshoe crab model, be sure to take a close look at its fascinating internal anatomy. First, the mass of tiny pastel green dots covering the interior of the shell are actually eggs thousands of horseshoe crab eggs. So without question, this model is of a horseshoe Cardinal Veins Cardinal Veins Heart crab female. A spawning female will lay up to 90,000 eggs in a spawning season. It is estimated that less than ten of these eggs will survive to adulthood. The elliptical cephalic artery goes to the brain, which looks like a black dot in this diagram. Female Horseshoe Crab The horseshoe crab is a true blue blood. Its blood, which contains copper, turns blue when exposed to air.