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1. Any of the group of bilaterally symmetric animals whose major indentation while they are still tiny embryos ultimately becomes their anus (e.g. clams, squids and insects), as opposed to their mouth, as in all other complex animals ('deuterostomes'--e.g. sea cucumbers, sea urchins and humans).

2. A person who spends far too much time talking shit and shitting on other people's ideas.
You know, I had taken you to be one of my species, but now I see you must in fact be a protostome; you definitely have an anus where your mouth should be.
by AKTT July 10, 2011
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