Fish Specimens. Cleared and stained skeletal preparations of the Antarctic silverfish (P. antarcticum), the blackfin icefish (C. aceratus), the yellowbelly rockcod (N. coriiceps), the threespine stickleback (G. aculeatus), and the zebrafish (D. rerio) at comparable stages of development. Bone is stained red with Alizarin red and cartilage is stained blue with Alcian blue. (A, B) C. aceratus, mid-larvae; (C, D)P. antarcticum, mid-larvae; (E, F) N. coriiceps, mid-larvae; (G, H) G. aculeatus, 10 dpf; (I, J) D. rerio, 6 dpf. Both ventral flat mounted (A, C, E, G, I) and lateral (B, D, F, H, J) views are shown. Note the lack of bony elements in pelagic notothenioid species compared to the benthic notothenioid and outgroups. The tree to the right of the images indicates evolutionary relationships. Abbreviations: bsr, branchiostegal rays; cbs, ceratobranchal cartilages; cb5, 5th ceratobrachial cartilage; ch, ceratohyal; cl, cleithrum; co, corocoid; dnt, dentary; ed, endochondral disk; fr, fin rays; hs, hyosymplectic; me, Meckel's cartilage; mx, maxilla; nc, neurocranium; op, opercle; ov, otic vesicle; pmx, premaxilla; pq, palatoquadrate; pt, pterygoid process of the palatoquadrate; te, teeth. Scale bars, 100 μm.