Editing Anus (section)

==Development==
{{main|Protostome|Deuterostome}}
In animals at least as complex as an [[earthworm]], the [[embryo]] forms a dent on one side, the [[blastopore]], which deepens to become the [[archenteron]], the first phase in the growth of the [[Gut (zoology)|gut]]. In deuterostomes, the original dent becomes the anus while the gut eventually tunnels through to make another opening, which forms the mouth. The protostomes were so named because it was thought that in their embryos the dent formed the mouth first (''[[wikt:proto-|proto–]]'' meaning "first") and the anus was formed later at the opening made by the other end of the gut. Research from 2001 shows the edges of the dent close up in the middles of protosomes, leaving openings at the ends which become the mouths and anuses.<ref>{{cite journal|title=Evolution of the bilaterian larval foregut |author=Arendt, D. |author2=Technau, U. |author3=Wittbrodt, J. |name-list-style=amp |journal=[[Nature (journal)|Nature]] |volume=409 |pages=81–85 |date=4 January 2001 |doi=10.1038/35051075 |pmid=11343117 |issue=6816|bibcode=2001Natur.409...81A |s2cid=4406268 }}</ref>