Caecilian amphibians have independently evolved a snake-like postcranial skeleton.
We analyzed Hox gene expression in embryos from a caecilian amphibian (Ichthyophis cf. kohtaoensis) which has a skeleton consisting of 126 vertebrae with the atlas being the only precloacal rib-less vertebra (Fig. 5, axial formula given in Table 2).
We examined expression of HoxC5, HoxA6, HoxC6, HoxB8, HoxC8, HoxC10 and HoxC13 and analyzed their expression in Brauer stage 26 embryos (unprocessed embryo shown in Fig. S1) and for the anterior genes we determined the exact anterior somitic levels of expression by labeling the somites through double immunostaining with MF-20 antibody.