Q.Name four protostomian phyla.

Protostomia and Deuterostomia are the two major evolutionary lines of the animal kingdom, distinguished chiefly by the fate of the embryonic blastopore.

During gastrulation in triploblastic, coelomate animals, an opening called the blastopore forms. Its fate divides the animal kingdom into two grand divisions:

1. Fate of the blastopore

• Protostomia ('mouth first'): the blastopore itself develops into the future mouth; the anus forms later, secondarily, at the other end.
• Deuterostomia ('mouth second'): the blastopore develops into the anus; the mouth is a new, secondary opening.

2. Cleavage pattern

• Protostomes: spiral and determinate (mosaic) cleavage — the fate of each blastomere is fixed early.
• Deuterostomes: radial and indeterminate (regulative) cleavage — each blastomere can still form a complete embryo if separated.

3. Coelom formation

• Protostomes are schizocoelous — the coelom arises as a split within the solid mesoderm. …