clade of animals whose mouth develops before the anus

Protostomes are a nephrozoan taxon of animals above the level of phylum. It is not part of the normal system of classification.

Temporal range: Ediacaran - Recent
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Subkingdom: Eumetazoa
Clade: ParaHoxozoa
Clade: Bilateria
Clade: Nephrozoa
(unranked): Protostomia
Grobben, 1908

They are a subtaxon of the Bilateria, and are contrasted with the deuterostomes. Protosomes are distingued by their embryo: in deuterostomes, the first opening (the blastopore) becomes the anus, while in protostomes it becomes the mouth.

DNA sequence analysis suggests that protostome animals can be divided into three major groups:

as well as a number of minor taxa, like the Chaetognatha.