A protostome is a type of animal in the kingdom Animalia that is characterized by a particular mode of embryonic development known as protostomy. The term "protostome" is derived from the Greek words "proto," meaning first, and "stoma," meaning mouth, as it pertains to the developmental sequence where the first opening to develop in the embryo becomes the mouth.
In protostomes, the early developing zygote undergoes a spiral cleavage pattern, resulting in cells that are not aligned directly over one another. As the embryo continues to develop, a cavity called the blastocoel is formed, which eventually becomes the digestive cavity or gut. During gastrulation, the blastopore, which is the initial opening formed during the process, develops into the mouth.
Additionally, protostomes are further characterized by exhibiting determinate cell fate during embryonic development. This means that each cell has a predetermined fate and is committed to forming a specific structure or tissue. Protostomes encompass a broad range of organisms, including arthropods (e.g., insects, spiders, crustaceans), mollusks (e.g., snails, clams, squid), annelids (e.g., segmented worms), and others.
Compared to deuterostomes, another major group of animals, protostomes differ in their developmental patterns and organization of body structures. Understanding the concept of protostome is crucial in the field of zoology and evolutionary biology to trace the origins and relationships of various animal species.
