The ocean has many unusual inhabitants, but few are as strange and ancient as the horseshoe crab. Get to know these living armored tanks that have roamed coastal seas for millennia.
1. Horseshoe crabs predate the dinosaurs.
Just how old are horseshoe crabs? Scientists have discovered fossils of their ancient ancestors that lived 445 million years ago. Dinosaurs first appeared about 200 million years later, during the Mesozoic era.
Horseshoe crabs went on to survive the extinction event that wiped dinosaurs from the planet 66 million years ago. Four species survive today — one found in the Atlantic coastal waters of North America and the Gulf of Mexico and three found in Asia’s coastal waters.
Horseshoe crabs have not evolved much in the past 200 million years, which is why they are often called “living fossils.”
2. Horseshoe crab blood is blue.
Human blood is red because our hemoglobin — the protein in red blood cells that transports oxygen around the body — contains iron. Horseshoe crabs have a different oxygen-carrying protein, called hemocyanin. Hemocyanin has copper rather than iron, which gives horseshoe crab blood its bright blue color.