Which of the following is an example of a protostome phylum where the mouth forms from the blastopore?

Which of the following is an example of a protostome phylum where the mouth forms from the blastopore?

• A. Echinodermata
• B. Porifera
• C. Mollusca
• D. Chordata

Answer: (C)

In protostome development, the mouth forms from the blastopore during early embryogenesis, and the anus develops later from another opening. Mollusks are a protostome phylum, so their embryonic blastopore becomes the mouth, making them the fitting example for this pattern. This contrasts with echinoderms and chordates, which are deuterostomes—the blastopore becomes the anus, and the mouth forms from a secondary opening. Porifera don’t undergo typical gastrulation in the same way, so they don’t illustrate this developmental pattern. So Mollusca is the correct example.

In protostome development, the mouth forms from the blastopore during early embryogenesis, and the anus develops later from another opening. Mollusks are a protostome phylum, so their embryonic blastopore becomes the mouth, making them the fitting example for this pattern. This contrasts with echinoderms and chordates, which are deuterostomes—the blastopore becomes the anus, and the mouth forms from a secondary opening. Porifera don’t undergo typical gastrulation in the same way, so they don’t illustrate this developmental pattern. So Mollusca is the correct example.