The answer on this question is pretty simple: most of the animals are. Of today known species, about 80% belong to the Phylum Arthropoda. Many of them are well-known, such as flies, ants, butterflies, beetles, spiders, scorpions, crawfish, crabs, millipedes, mantids and so on...
There also are groups of animals with less reputation in the arthropods though. e.g. sea spiders, pseudo-scorpions and whipspiders are commonly only known to a specific circle of persons.

The Phylum Arthropoda is structured in four Sub-Phyla. The insects (Insecta/Hexapoda), centi- and millipedes (Myriapoda), shellfishes (Crustacea) and arachnids (Arachnida). The largest group of arthropods are the insects, who put up the largest order of animals there is, namely the beetles (Coleoptera).

Whoever only feels disgust in the face of the given diversity and ingenious conformity shown by these animals, should make himself aware in which world he is living: the world of the arthropods...

F. Schramm