The fossil record of xiphosurans extends back to the Late Ordovician, or around 445 million years ago. For modern horseshoe crabs, their earliest appearance was approximately 250 million years ago during the … 展开

Like all arthropods, horseshoe crabs have segmented bodies with jointed limbs, which are covered by a protective cuticle made of chitin. They have heads composed of several segments, which eventually fuse as an embryo. … 展开

In the modern day, horseshoe crabs have a relatively limited distribution. The three Asian species mainly occur in South and Southeast Asia along the Bay of Bengal and the coasts of Indonesia. A notable exception is the … 展开