Fig. 2

Alternative hypotheses for ecdysozoan relationships based on molecular data from expressed sequence tags (after Dunn et al. 2008), depicting Panarthropoda as variably having multiple evolutionary origins (a tardigrades within Cycloneuralia) or a single evolutionary origin (b tardigrades sister to Onychophora + Arthropoda). Characters involving segmentation are mapped onto cladogram b as follows: 1 paired segmental ventrolateral appendages, 2 paired leg nerves, 3 Engrailed gene expressed in posterior ectoderm of each segment (Gabriel and Goldstein 2007), 4 segmented leg musculature (Schmidt-Rhaesa and Kulessa 2007), 5 commissures in ventral nerve cord (Zantke et al. 2008), 6 segmented nephridia (Mayer 2006), 7 commissures in ventral nerve cord in segmental register/rope–ladder nervous system (Mayer and Harzsch 2007), 8 segmented neurons show a reaction to serotonin (Mayer and Harzsch 2008), 9 Pax protein has a pair-rule function (Gabriel and Goldstein 2007)