Figure 1.

Phylogenetic scheme of the major arthropod groups and modes of head segmentation. The phylogeny depicted is based on molecular data (4, 5); the depiction of the head segments represents a consensus from textbooks (1, 34). The segments are labeled according to the conventions in the respective taxa; leg-bearing segments are shaded. The position of the mouth is indicated by a black oval. The presumed missing segment in the chelicerates is marked with an “x”. The drawing is modified from Willmer (34).