Arachnid and that there may be up to 600,000 in total. Arachnid Arachnids () are a class (Arachnida) of joint-legged invertebrate animals (arthropods), in the subphylum Chelicerata. Almost all adult arachnids have eight legs, although the front pair of legs in some species has converted to a sensory function, while in other species, different appendages can grow large enough to take on the appearance of extra pairs of legs. The term is derived from the Greek word ("aráchnē"), from the myth of the hubristic human weaver Arachne who was turned into a spider. Spiders are the largest order in the class,
Small shelly fauna mostly of unknown origin. However it is known that some, including "Microdictyon", were produced by lobopods, animals that looked like worms with legs and are thought to be close to the ancestors of arthropods. Univalved and bivalved shells are fairly common. Some cap-shaped shells are thought to be the only sclerite covering their creators, while others are known to be parts of a more complex armor system like "Halkieria"’s. The Helcionellids are thought to be early molluscs with somewhat snail-like shells. Some have horizontal "exhaust pipes" on the concave edges of their shells, and there is debate about whether these