Arthropods are a large group of organisms that have exoskeletons that contain chitin, and jointed legs. They too, have segmented bodies, especially in the larval stage. Arachnids , such as ticks and spiders, and insects , such as bees, roaches, and crickets. Insects all have three pairs of legs. Echinoderms Echinoderms are actually more closely related to chordates than tosome of the other animal phyla.
Adult echinoderms have five-fold radial symmetry, but embryonic echinoderms have bilateral symmetry.
The simplest chordates are the lancelets and tunicates, which have a notochord, but no backbone. All other chordates have backbones and are classified as vertebrates. Sharks and rays don't have calcified bones in their skeletons, but all other groups have hard bones. Frogs are examples of vertebrates. See the development of a chick embryo.