From ZooTerms (Dictionary of Invertebrate Zoology)
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orifice (noun; Latin os, mouth; facere, to make): 1. An opening into a cavity; a mouth-like opening.

2. (Arthropoda: Crustacea) In sessile Cirripedia, the opening in the wall occupied by the operculum

See also: aperture. 3. (Bryozoa) The opening on the margin of the orificial wall through which the lophophore passes.