Fig 1. Procrustes distance and axes definition.

(A) For Procrustes analysis, two landmark-sets, morph A and morph B, with an equal number of vertices (points) are required. Procrustes analysis allows to bring these two landmark sets in the best overlapping fit without changing their relative positions, using at least pan and rotation. This is called partial Procrustes fit and allows comparisons of form. If in addition to pan and rotation also scaling is adjusted, the result is a full Procrustes fit and allows shape analysis. Double-headed arrows give point-wise Procrustes distances, which are minimized during the analysis. The average Procrustes distance is the mean length of all arrows. Landmark-sets that differ only in scaling would overlap perfectly using full Procrustes, leading to a Procrustes distance of zero. (B) For the analysis of alterations, daphnids are inspected direction-wise: The dorso-ventral body axis is represented by the x-axis, with positive values towards the dorsal end. The longitudinal body axis is represented by the y-axis, with positive values towards the head. The lateral body axis is represented by the z-axis, with positive values out of the drawing plane, towards the viewer.