Arthropoda
Arthropods are invertebrates that have exoskeletons, segmented bodies, and jointed appendages. The phylum arthropoda includes insects, arachnids, and crustaceans. They have rigid outer shells that inhibits growth which the alleviate by replacing periodically by moulting. Arthropods body plans are repeated segments, with each segment having a pair of appendages. Arthropods have the most species in most environments because of their versatility and survivability. Arthopoda contains over a million species, making up more than 80% of all living animal species, and they are also one of two animal groups who are very successful in dry environments. They range in size from microscopic plankton up to a few meters long.