The functional significance of aperture form in gastropods

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Abstract
Aperture form of marine prosobranch gastropods has evolved under the influence of a number of different selective forces, including: generation of shell form; protection from predation; accommodation of the foot during clamping behavior; and accommodation of water currents in and out of the mantle cavity. Aperture form correlates positively with foot shape in most gastropods and foot shape, in turn, correlates moderately well with substrate preference. Almost all gastropods that have non-round apertures elongate the aperture parallel to the foot so that water currents tend to flow anteriorly to posteriorly. Freshwater pulmonates have responded to somewhat different stresses. They exhibit clamping behavior and show correspondence between foot shape and aperture shape. They show less apertural strengthening as crab (or crayfish) predication in less of a factor and presumbly because calcium carbonate is available. They also lack anterior-posterior apertural elongation due to the absence of water currents through their mantle cavity. Due to the absence of mantle cavity water currents and clamping behavior, terrestrial gastropods do not show the apertural modifications associated with these 2 factors. Few adaptations of apertural form are present to resist predation. Many of the apertural modifications of terrestrial pulmonates seem to be concerned with the problems of water loss during estivation.