Aptico

thumb|upright 2.0|Some examples of aptychi (top right: Oppelia from Late Jurassic of Solnhofen, Germany; bottom left: aptychi (recto and versus) from Late Jurassic of Lombardy, Italy), and conceptual scheme of their function if indeed they were used to close the shell aperture, as opposed to being jaws. thumb|One of what would have been a pair of aptychi (at first given the name Trigonellites|Trigonellites latus and described as a bivalve) from the [[Kimmeridge Clay Formation in England]]