Why do horseshoe crabs have tails

They can grow to be 18 to 19 inches 46 to 48 centimeters from head to tail, while the males are approximately 14 to 15 inches 36 to 38 centimeters. The horseshoe crab species found around the United States Limulus polyphemus lives in the Atlantic Ocean along the North American coastline. There are three other species of horseshoe crab worldwide, which are located in the Indian Ocean and in the Pacific Ocean along the coast of Asia. Horseshoe crabs utilize different habitats depending on their stage of development.

The eggs are laid on coastal beaches in late spring and summer. After hatching, the juvenile horseshoe crabs can be found offshore on the sandy ocean floor of tidal flats. Adult horseshoe crabs feed deeper in the ocean until they return to the beach to spawn. Many shorebirds, migratory birds, turtles, and fish use horseshoe crab eggs as an important part of their diet.

Horseshoe crabs are a keystone species within the Delaware Bay ecosystem. Horseshoe crabs like to dine at night on worms and clams, and may also eat algae. A horseshoe crab picks up food with appendages located in front of its mouth. Because it has no mandible or teeth, the horseshoe crab crushes food between its legs before passing it to the mouth.

During the late spring and early summer, adult horseshoe crabs travel from deep ocean waters to beaches along the East and Gulf coasts to breed. The males arrive first and wait for the females. When the females come to shore, they release natural chemicals called pheromones that attract the males and send a signal that it's time to mate. Horseshoe crabs prefer to breed at night during high tides and new and full moons.

The males grasp onto the females and together they head to the shoreline. On the beach, the females dig small nests and deposit eggs, then the males fertilize the eggs. The process can be repeated multiple times with tens of thousands of eggs. Towards the front of the prosoma is a small ridge with three dark spots. Two are the median eyes and there is one endoparietal eye.

Each of these eyes detects ultraviolet UV light from the sun and reflected light from the moon. They help the crab follow the lunar cycle. This is important to their spawning period that peaks on the new and full moon. Two ventral eyes are located near the mouth but their function is unknown. Multiple photoreceptors located on the telson constitute the last eye.

These are believed to help the brain synchronize to the cycle of light and darkness. Check out a diagram of the horseshoe crab's 10 eyes. A horseshoe crab absorbs oxygen from the water using gills that are divided into 5 distinct pairs located under the abdomen. Each pair of gills has a large flap-like structure covering leaf-like membranes called lamellae.

Gaseous exchange occurs on the surface of the lamellae as the gills are in motion. Each gill contains approximately lamellae that appear as pages in a book.

They are commonly called book gills. The gills also function as paddles to propel juvenile horseshoe crabs through the water. The horseshoe crab has 6 pairs of appendages on the posterior side of the prosoma. Large numbers of adults crawl up onto sandy, protected beaches to mate and lay eggs. Females lay clusters of about 4, greenish eggs in the sand around the high-tide mark.

They return to the beach to lay more eggs during high tides throughout the season. Eggs take about one month to develop and hatch. Young swim to shallow, sandy, protected nursery areas, where they remain for up to two years. Horseshoe Crab Limulus polyphemus.

Young horseshoe crabs are sand-colored. If you see horseshoe crabs mating and would like to report a sighting, please visit the Report Sightings page for more information. No, horseshoe crabs are in a class by themselves; they are more closely related to spiders, scorpions, and ticks. They are different from true crabs because they have no antennae and no mandibles mouth parts for grinding food.

Like spiders, they have a pair of chelicerae small appendages for moving food into the mouth. Yes and no, that idea comes from the fact that million years ago, ancestors of horseshoe crabs were abundant. The anatomy of the species we have today is not much changed from those older forms.

The life span of an individual horseshoe crab is not millions of years, but they can live up to 20 years! Horseshoe crabs do not bite or sting. Despite the ferocious look of the tail, it is not used as a weapon. Instead, horseshoe crabs use their tails for righting themselves if they are flipped over by a wave.

They do have spines along the edge of their carapace, so if you must handle them, be careful and pick them up by the sides of the shell, not the tail. The are not picky eaters, they eat almost anything.

They feed on small clams, crustaceans, and worms; however, they will also eat other animals and even algae. Because they have no mandibles or teeth, they crush hard food between their legs before passing it to their mouth. Like birds, horseshoe crabs also have gizzards for grinding food before it reaches their stomachs. Only horseshoe crabs have a blood-clotting agent known as Limulus Amebocyte Lysate, or LAL, which clots in the presence of certain groups of bacteria. These bacteria are difficult to detect by other means.