blastopore
blastopore
A jellyfish
A diaphragm in optics, including telescopes, is a thin opaque structure with a central opening.
In deuterostomes, the first opening that develops during embryonic development is called the blastopore. This opening typically develops into the anus, while the mouth forms later from a secondary opening. This is in contrast to protostomes, where the blastopore usually becomes the mouth. Examples of deuterostomes include chordates and echinoderms.
dens
Esophagus
lumen - the central opening within a tube or hollow organ.
It all depends on the structure. In cell biology it can be a pore or a stomata.
arch
xylem
Vocal chords.