An arthropod is an invertebrate animal that has an exoskeleton, a segmented body, and jointed appendages. They include insects, arachnids , and crustaceans. Arthropods range in size from microscopic to many meters long. Most arthropods lay eggs but few give birth to live young. Many arthropods undergo molting. A process where the animal will shed its exoskeleton to make room for a new one. There are millions of species. Most arthropods have a body separated into three segments: The head, thorax, and, abdomen. This is the Brazilian Wandering Spider, the most venomous spider in the world.