Which phylum is categorized as protostome in embryonic development?

• A. Annelida
• B. Echinodermata
• C. Cnidaria
• D. Porifera

Answer: (A)

Protostomes share a developmental pattern where the embryo undergoes spiral, determinate cleavage, the blastopore typically becomes the mouth, and the coelom forms by schizocoely. Annelids fit this pattern as segmented worms that develop through these protostome traits. Echinoderms are deuterostomes, meaning they exhibit radial cleavage and the blastopore becomes the anus first, with coelom formation by enterocoely. Cnidarians are diploblastic with radial symmetry and do not follow the protostome pattern. Poriferans lack true tissues and aren’t classified by protostome/deuterostome development. So, the phylum that is protostome is Annelida.