The horseshoe crab has been one of my favorite undersea creatures ever since I encountered this unusual animal years ago at an aquarium’s touch tank. Instructions were given on how to gently interact with the harmless, rounded, long tailed creatures and I along with a group of children stuck our hands into the water to rub their backs and let the strange looking animals crawl over our hands. At that time, I had no idea that these unusual animals may have already saved my life, many times over. Here are some fun facts about these amazing arthropods.
Fun Facts about the Incredible Horseshoe Crab : Ancient History
Along with the Ginkgo Tree, Triops, and a few others, the horseshoe crab is one of a few species alive today known as living fossils. Fossils have shown that horseshoe crabs have changed little since the Paleozoic Era ( about 542 – 251 million years ago ). Although Triops are a similar looking they are not thought to be closely related to horseshoe crabs.
Fun Facts about the Incredible Horseshoe Crab : What’s in a Name?
The horseshoe crab’s scientific name has changed over time from Limulus cyclops, Xiphosura americana, and Polyphemus occidentalis. To the scientific community, the four species are currently known as Limulus polyphemus, Carcinoscorpius rotundicauda, Tachypleus tridentatus, and Tachypleus gigas. Common names for these unusual animals are horsefoot, king crab, helmet crab, or saucepan. The names are derived from the shape of the horseshoe crab’s shell, large size, and its resemblance to crabs.
Fun Facts about the Incredible Horseshoe Crab : When is a Crab not a Crab?
The horseshoe crab is not a true crab or even a Crustacean. While they are both Arthropods, this living fossil is classified under the class Merostomata ( order Xiphosura ) and may be the closest living relatives to Trilobites which lived over 500 million years ago. Spiders and ticks are believed to be the closest present day relatives to the four known species of horseshoe crab.
Fun Facts about the Incredible Horseshoe Crab : Unusual Anatomy
The horseshoe crab has ten eyes or light sensing organs. They are located on it’s top, bottom, and tail. Of the seven eyes on the top of the shell, two compound eyes on opposite sides are most obvious. Aside from this living fossil, compound eyes are not known on any other living chelicerates, like spiders, scorpions, mites, and ticks. Behind those are two smaller eyes, three eyes are on the front middle of the shell, two eyes are on the bottom of the unusual animal, and on the tail there are photoreceptors (counted as one eye). The horseshoe crab can sense UV light.
This special creature also has many legs and book gills. While true crabs have five pairs of appendages, six walking legs and two claws, the unusual animal called the horseshoe crab has six pairs : five pairs of walking legs and one pair of chelicerae. The first pair of walking legs can be used to differentiate males from females. This underwater animal can use its legs to pull itself out of the water and the book gills, which aid in swimming, also allow these special animals to breathe on land for short periods as long as they stay moist. This is important as this undersea creature mates and lays her eggs on land, in the shore’s moist sand. The long tail is harmless and used to help the horseshoe crab flip over.
Fun Facts about the Incredible Horseshoe Crab : Where Horseshoe Crabs Live
Four species of horseshoe crabs live in different areas of the Atlantic, Indian, and Pacific Oceans. The Atlantic species is often seen in the Gulf of Mexico and migrates to Delaware Bay to breed. It also makes rare appearances in Europe.
Fun Facts about the Incredible Horseshoe Crab : Modern Day Miracle or Medical Marvel
This unique creature has saved countless lives, maybe even your own. If you’ve ever received an injectable vaccine or injectable medical drug treatment you owe some thanks to this strange animal. The horseshoe crab’s blue blood provides a way to test bacterial contamination in intravenous fluids. That means, the horseshoe crab may have saved your life, without you even knowing it. The unusual animals are collected, blood is taken, and the creatures are released back to the wild they came from.
Fun Facts about the Incredible Horseshoe Crab : Controversy
According to horseshoecrab.org studies have shown that the blue blooded animals can survive a bleeding, continue to reproduce, and can be collected year after year for blood collection. However, studies have also shown that between 3% – 15% do die. Mortality rates are affected by the horseshoe crab collection process and handling afterwards. There are still questions about what total effect this may be having on the special animals as well as their offspring and numbers produced after blood has been collected. Valuable medical research is currently dependent on the survival of these unique creatures.
Fun Facts about the Incredible Horseshoe Crab : The Horseshoe Crab and The Red Knot
A sharp decline in numbers of a small shore bird known as the Red Knot brought attention to a decrease in horseshoe crab numbers. The Red Knot has the longest known migration of any bird and has been found to be dependent on the nourishment of horseshoe crab eggs to reach its destination. Other shorebirds that eat horseshoe crab eggs and Sea Turtles that eat the adults are horseshoe crab predators.
Fun Facts about the Incredible Horseshoe Crab : Survival of the Horseshoe Crab
The four species of horseshoe crab are part of ecosystems from the east to west. These living fossils are threatened due to habitat loss over fishing. This creature has survived millions of years but numbers have started to decline.
Fun Facts about the Incredible Horseshoe Crab : The Horseshoe Crab May Have Saved Your Life
You might not have realized it, but the horseshoe crab has probably made a difference for you, keeping you healthy, and may have even saved your life. You can repay this amazing animal in two easy ways. 1. Keep trash out of the ocean by not littering. 2. If you see this unusual animal on its back struggling to turn over, help it back onto its legs.
PBS Nature special on The Red Knot & Horseshoe Crab – Crash: A Tale of Two Species