The inner envelope or membrane surrounding tissue or organs, or in some organisms, an inner sheath-like structure.
From endo- (Greek 'within') + theca (Greek 'case' or 'sheath'). Used in anatomy and zoology since the 1800s.
In coral polyps, the endotheca is the inner wall that separates the animal tissue from the calcium carbonate skeleton it builds, making it the interface between biology and geology!
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