What Is the Primary Distinction Between Protostomes & Deuterostomes?

Starfish are deuterostomes.

Biologists divide the animal kingdom into several phyla based on the presence of true tissues and how their body plans develop. Within the phyla that have a one-way, two-ended digestive tract, the animals are further classified as protostomes or deuterostomes.

Distinction

The opening of the digestive tract in an embryo is called the blastopore. The primary difference between protostome and deuterostomes concerns whether the blastopore becomes a mouth or an anus. Protostome means "mouth first," reflecting the fact that in this type of animal, the embryo first forms a mouth from the blastopore and then later forms an anus. In deuterostomes, meaning "mouth second," the anus forms from the blastopore and the mouth follows later.

Cleavage

Deuterostomes have indeterminate cleavage, every early cell is the same. A cell taken from a four-cell embryo could form a whole new embryo by cell division. Protostomes have determinate cleavage, cells differentiate and if isolated, are capable of forming a normal new embryo.

Examples

Echinoderms and chordates, which include mammals, are a few examples of deuterostomes. arthropods, annelids and mollusks are examples of protostomes.

References

• San Francisco State University: Biology-Animal Body Plans
• University of New Mexico: Biology Lab