Living fossils that haven't changed for millions of years

Horseshoe crab ( Limulidae )

Horseshoe crabs first appeared more than 300 million years ago, making them older than the non-avian dinosaurs. They haven’t evolved much in that time. While horseshoe crabs look a lot like prehistoric crabs, they’re more closely related to spiders and scorpions.

Of the four species of horseshoe crabs, the Atlantic horseshoe crab (Limulus polyphemus) lives in the Atlantic coastal areas of North America and Central America, and the three Indo- Pacific species of horseshoe crabs ( Tachypleus gigas ), Tachypleus tridentatus , and Carcinoscorpiu rotundicauda are found in coastal areas of Asia.

Horseshoe crabs have a very hard exoskeleton, 10 legs for crawling on the seabed, and a pair of pincers used to bring food to their mouths. Their blood contains a special protein that turns blue when exposed to oxygen. Therefore, horse blood is often used in medical research to develop vaccines. Photo: Wikipedia

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