This is a male Tri-spine horseshoe crab - Tachypleus tridentatus, which are the largest species of horseshoe crab. Horseshoe crabs have lived for over 450 million years and have survived 5 mass extinction events including the asteroid that killed the dinosaurs.
Horseshoe crabs are actually more closely related to spiders and scorpions.
They have 10 legs and 9 eyes in different locations on their body. The 2 largest compound eyes help them find mates.
Their spines are used for protection and are moveable and their large tail (telson) is used to right themselves.
Males are typically 20% smaller than females and have thickened claws to clasp themselves onto the back of the female during mating and are shaped to fit over the female's carapace.
Females tend to be larger than males. Rubbed and worn shells on females are mating scars from where the male has mounted the female.
