A group of living things
Spiders and kin
Chelicerata
Fang mouths, jointed legs and no feelers.
Its members' last common ancestor lived about 500 million years ago.
You and spiders and kin last shared an ancestor about 580 million years ago (on 11 November, if life's history were one year).
These are the fang-mouthed arthropods: spiders, scorpions, mites and horseshoe crabs. The big surprise is the horseshoe crab. It looks like a crab, but it is not a true crab. It is closer to spiders and scorpions. They all have a hard outer shell and jointed legs. But unlike their cousins the insects and crustaceans, they have no antennae, and their small front mouthparts form fangs or tiny claws.
Most have a body with two main parts, a front section with the mouth and legs and a rear section behind. Spiders have eight walking legs, usually eight eyes, and silk makers at the back end. Scorpions hold a pair of large pincers forward and carry a stinger at the end of a curved tail. Mites and ticks are mostly tiny, with rounded bodies and no slim waist.
Most live on land. Spiders hunt in gardens, forests, deserts and houses, while horseshoe crabs live in shallow coastal seas. Living members range from tiny face mites smaller than a full stop to horseshoe crabs up to about twice as long as a school ruler. The oldest fossils of horseshoe crab relatives are about 445 million years old, far older than the dinosaurs.
Glowing hunters
Scorpions glow blue-green under ultraviolet light from a special torch, so researchers can spot them at night.
Face mites
Tiny eight-legged mites live in the hair roots and oil glands of the human face, and in one study DNA traces were found on every adult over 18 tested.
Blue blood
Horseshoe crab blood is blue and clots around traces of bacteria, so it is used to check that vaccines, medicines and medical tools are clean.