Abstract
It is named after the clausilium, a door-like movable plate, connected to the columella by a long and flexible stalk. In combination with apertural lamellae, the clausilial plate closes the aperture of the shell when the soft body of the snail is with drawn. It is generally assumed that a CA as such originated only once in the course of evolution. 1 However, after its basic structures had formed, various adaptive refinements of the CA may have evolved more than once independently. 4 In this note a hitherto overlooked example of such a homoplasious development is reported. Recently, Giusti et al . 5 published excellent photographs (figures 326‐329, 338‐344) of shells of Lam pedusa melitensis (Caruana Gatto, 1892), with details of the CA. In this species the columella is con spicuously broadened within the body whorl, to form a ‘columellar knob’. 5
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