Horseshoe crabs are arthropods that are often referred to as living fossils due to their long evolutionary history. However, there are a few other terms that can be used to describe these unique creatures. For instance, some people refer to them as chelicerates, which is a reference to their claw-like appendages. Another synonym for horseshoe crabs is limulus, which is derived from their scientific name, Limulus polyphemus. Additionally, they are sometimes referred to as sea spiders, although they are not true spiders and are more closely related to scorpions and ticks. Regardless of the term used, horseshoe crabs remain an important species for studying and understanding the natural world.