What type of organism is characterized by a mouth forming before the anus?

The organism characterized by a mouth forming before the anus is known as a protostome. In protostome development, the first opening that forms during embryonic development becomes the mouth, while the anus is formed later from a different opening. This is a fundamental aspect of their developmental biology and distinguishes them from deuterostomes, where the anus develops before the mouth.

Protosomes include a wide range of organisms, such as arthropods, mollusks, and annelids. Understanding this developmental characteristic is essential in differentiating between various animal groups and their evolutionary pathways.