Protostomia is a major group in the animal kingdom that includes a wide variety of organisms, such as arthropods, mollusks, and annelids. These animals are characterized by their embryonic development, where the mouth forms before the anus during the early stages of growth. This group is distinguished from Deuterostomia, where the anus develops first. Protostomes are typically divided into two main clades: Lophotrochozoa and Ecdysozoa. Lophotrochozoans include animals with a lophophore or a trochophore larval stage, while ecdysozoans are known for their ability to molt their exoskeletons. This diverse group plays a crucial role in ecosystems and includes both invertebrates and some of the most familiar animals.