Non-predatory shell damage in recent deep-endobenthic bivalves from Spain

Shells of deep-endobenthic bivalves from several localities of the Spanish littoral are affected by various modalities of shell damage, which cannot be attributed to the direct activity of predators. The frequency and morphology of these damage features, together with the results of tests with living specimens, indicate that they are brought about by the process of burrowing. Selected aspects of their distribution at the individual and population level also allow us also to differentiate at least two indirect origins for them: scape movements from predators and readjustments to storm-induced changes in the sediment column. As expected, the first cause is likely only for some taxa from sheltered coastal environments, while the second applies to all samples from exposed shores. Within this pattern, some shell features are recognized, at least in part, as adaptations to minimize shell damage. Divaricate ribs in Solecurtus strigilatus seem to perform such a function by acting as directions of structural weakness.