Horseshoe Crab
Tags: Horseshoe, Crab
The Sea Scorpions (technically known as "Eurypterids") are a group of extinct arthropods. The earliest known fossils of these animals date back to the Ordovician period, about 460 million years ago. However, they probably evolved while the earlier Cambrian period, perhaps nearby 510 million years ago (although no actual fossils of Sea Scorpions from this time have been found, trace fossils which are suggestive of their nearnessy have been found).
The Sea Scorpions were water-living animals, although it is plan possible, even likely, that some species may have lived an amphibious lifestyle, and perhaps even been able to breath in both water and air. The earliest species evolved and lived in the warm shallow seas, but later varieties of Sea Scorpion favorite brackish water or freshwater. Despite this change in habitat, these animals continued to survive and evolve until the end of the Paleozoic Era, only ultimately going extinct while the Permian-Triassic mass extinction.
Sea Scorpions were not undoubtedly true scorpions, although it is believed that that they may have been connected to arachnids and horseshoe crabs. In the past, they have sometimes taxonomically settled in the same class as the horseshoe crabs, namely "Merostomata", but today, they are usually settled in their own separate class "Eurypterida".
Physically these animals had a carapace with paddles (which were used for swimming and perhaps digging), a body with twelve segments, and a tail. The tail usually tapered and ended with a spike (it is not clear if this could have been venomous), and the animal also had eight jointed legs. Most Sea Scorpions were quite small, about 8 inches (20 centimeters) or less in length, but there were also some titanic varieties too, which grew to as long as 6 to 8 feet (2 to 2.5 meters)!
Sea ScorpionsHorseshoe Crab at the Denver Zoo Video Clips. Duration : 0.97 Mins.