Results of general linear modelling of the regression between shell shape and water depth.

Three models were tested: simple, regression independent of nominal taxonomic grouping; parallel, regression slope is independent of taxonomic grouping, but the intercept is not; non-parallel, slope and intercept depend on taxonomic grouping. The p-values on F-statistics indicate the probability that the simpler model in each comparison is adequate; significant p-values indicate that the more complex model is preferred (see text). In each comparison the more complex model is supported and, overall, the non-parallel model is preferred, indicating a correlation between depth and morphology.