The Triple Taxonomic Deception

The ultimate taxonomic bamboozle! Horseshoe crabs are living fossils that have existed for 450 million years, yet their name is a triple deception. These marine arthropods are neither horses (obviously), nor shoes (despite their helmet-like appearance), nor crabs (they're actually closer relatives to spiders and scorpions than to true crabs)! They belong to the subphylum Chelicerata, making them more arachnid cousins than crustacean buddies. Their blue copper-based blood is so valuable for medical testing that it's worth $15,000 per quart. Evolution really said "let's make something that defies all naming conventions" and then never changed the design for half a billion years because it was just that good.