Sentence:  We can distinguish therefore in the body of a polyp the column, circular or oval in section, forming the trunk, resting on a base or foot and surmounted by the crown of tentacles, which enclose an area termed the <WSD>peristome</WSD>, in the centre of which again is the mouth. ... The mouth may be level with the surface of the <WSD>peristome</WSD>, or may be projecting and trumpet-shaped. 
Meaning of the word marked with <WSD> tags:  The parts of or surrounding the mouths of numerous invertebrates.