Arthropods have a hard outer shell, or exoskeleton, which is periodically shed and regrown. The body is segmented, usually with 2-3 distinct groupings. Paired and segmented appendages are usually present.
With the exception of insects, arthropods undergo little to no metamorphosis. Immature arthropods resemble adults. A few crustaceans have a immature form that differs significantly from that of the adult. Some Celicerata have fewer legs in the immature form.
Arthropod habitats are very diverse. Arthropods are found in almost every habitat. Feeding is equally varied.
Number of species
There are 104,000 species found in North America, and 840,000 worldwide.
There are 4 subphylums in this phylum.