Protostome
Protostomes are a major lineage of animals in which the mouth forms from or near the first opening of the embryo, the blastopore, during early development. In contrast, deuterostomes typically form the anus from the blastopore and later develop the mouth. Protostomes comprise two large clades, the Lophotrochozoa and the Ecdysozoa, and include most animal species such as mollusks, annelids, arthropods, and many nematodes.
Embryology and body plan are hallmarks of protostomes. They typically exhibit spiral, determinate cleavage of the
Larval forms and features vary across protostomes. Several groups have free-swimming trochophore-like larvae, especially within the
Examples and significance: The protostome lineage includes Mollusca, Annelida, Arthropoda, Nemertea, Platyhelminthes, and Nematoda, among others.