noun
- animals in which the mouth develops from the first opening (blastopore) that forms during embryonic development
Usage: biology; zoology
Examples
- Protostomes include arthropods, mollusks, and annelids.
- In protostomes, the blastopore becomes the mouth during development.
- Scientists classify most invertebrates as protostomes.
- The evolutionary split between protostomes and deuterostomes occurred millions of years ago.
- Insects and spiders are examples of protostomes.
- Protostomes show spiral cleavage during early embryonic development.