Fig. 7

Four different topologies with the evolutionary plate transformations on segment 1, optimized in three most parsimonious (a–c) and one less parsimonious (d) ways. The putative transformation series goes through following stages: (1) segment composed of a closed ring (putative ground pattern), (2) segment composed of one tergal and one sternal plate, (3) segment composed of one tergal plate and a partially differentiated sternal plate, (4) segment composed of one tergal plate and sternal plate differentiated into one midsternal and two episternal plates