Arthropods

Anthropods are invertebrates that make up for the lack of backbone with an exoskeleton. They have segmented bodies and jointed appendages. They also have bilateral symmetry (vertical symmetry) and an open circulatory system. Of the estimated 5-10 million species, some known examples are Black Widow spider (Latrodectus) and the Four Spotted Skimmer dragonfly (Libellula quadrimaculata).