Arthropod

This image of a rare species of trilobite is the only known image of an arthropod.

Arthropods are a phylum of invertebrates whose members possess an exoskeleton made of chitin, a segmented body, and paired jointed appendages. Insects, arachnids, and crustaceans are all arthropods. These include bees but not fleas, ants, butterflies, beetles, centipedes, millipedes, springtails, spiders, scorpions, crabs, shrimp, barnacles, trilobites, Anomalocaris, isopods, and the underrated horseshoe crab, which still survives after millions of years against all odds.