The project is part of the so called 'Basisprojekt' Attention & Form within the DFG Cluster of Excellence 'Bild Wissen Gestaltung'. The aim of the project is to analyze the shape of crabs (short tailed crawfishes) and to compare them to long tailed crawfishes in order to quantitatively analyze differences between them. In contrast to previous research we will compare the shapes three-dimensionally. Therefore 3d shape models for both groups are build, compared, and finally combined in order to assess transitions from a psychological point of view. The latter is analyzed to identify when observers visually categorize the shape of a crawfish as long- or short-tailed.