Which groups exhibit protostome embryonic development?

Which groups exhibit protostome embryonic development?

• A. Nematoda and Rotifera
• B. Nematoda only
• C. Rotifera only
• D. Neither

Answer: (A)

Protostome development is defined by how the embryo divides and what the blastopore becomes. In protostomes, cleavage is typically spiral and determinate, and the mouth forms from the first opening (the blastopore). Nematodes fit this pattern: their early cell divisions are determinate, and the blastopore becomes the mouth as the embryo develops, even though they lack a true coelom. Rotifers also follow a protostome-type pattern, with determinate, mosaic-like cleavage and the mouth arising from the blastopore. In contrast, deuterostomes form the anus from the blastopore first, with the mouth developing later, which is not the pattern here. Because both nematodes and rotifers exhibit this protostome developmental sequence, they are the groups described.

Protostome development is defined by how the embryo divides and what the blastopore becomes. In protostomes, cleavage is typically spiral and determinate, and the mouth forms from the first opening (the blastopore). Nematodes fit this pattern: their early cell divisions are determinate, and the blastopore becomes the mouth as the embryo develops, even though they lack a true coelom. Rotifers also follow a protostome-type pattern, with determinate, mosaic-like cleavage and the mouth arising from the blastopore. In contrast, deuterostomes form the anus from the blastopore first, with the mouth developing later, which is not the pattern here. Because both nematodes and rotifers exhibit this protostome developmental sequence, they are the groups described.