Biology / Unit 10 Bio 2225 short lesson, about 20 seconds
Protostome versus Deuterostome Development
Captions available
The idea
In a protostome embryo, the first opening becomes the mouth; in a deuterostome embryo, that opening becomes the anus, with the mouth forming second.
In practice
A mollusk's earliest opening becomes its mouth, protostome-style, while a sea star's earliest opening becomes its anus instead.
Where people slip
This criterion sorts bilaterians by developmental sequence, not mouth position — the defining event happens before the adult body forms.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
Builds on
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