Morphospaces are quantitative representations of phenotype space that have proved particularly useful in the broad field of evolutionary morphology. Yet, do current conceptualizations of morphospaces appropriately echo the evolutionary dynamics of organisms depicted in such spaces? Many studies implicitly consider the phenotype space as an isotropic state-space, but several lines of evidence suggest that such a view is inadequate. In particular, advances in evolutionary developmental biology have shed light on the statistical properties of the genotype-phenotype map and their consequences for the structure of variation. Here, I use a trilobite case study to illustrate the effect of constraints on the accessibility structure of phenotype space. The morphospace obtained is strongly anisotropic and reveals discordances between the apparent range of possible phenotypes and their actual accessibility. It is advised that geometric measures of distance in morphospace should be taken with caution and complemented with developmentally meaningful measures of evolutionary accessibility.