(a) Somites of a S24 skate embryo showing (a') trunk (tr), cloacal (c), and tail (tl) somites, delineated with dashed lines. (b) A cleared and stained vertebral column from a skate hatchling, with the trunk to tail transition denoted with an asterisk. (c) µCT scan reconstruction of skate trunk and (d) tail vertebrae, with vertebral elements corresponding to a single body segment color-coded blue or yellow, neural tissue colored green, and blood vessels colored red. Note that in (d), one set of spinal nerves spans two vertebrae. a/v, caudal artery and vein; ca, outer cartilage of vertebral body; ce, centrum; ha, haemal arch; ia, intercalary arch; na, neural arch; nsp, neural spine; sc, spinal cord; sn, set of spinal nerves; tp, transverse process. Scale bars: (a) 400 µm; (a') 100 µm; (b) 500 µm; (c) and (d) 100 µm.