Fig. 1

Earliest ontogenetic characters on both dorsal and ventral valves of Eohadrotreta zhenbaensis from South China. a, f, g conjunct juvenile valves, showing the protegulum and two pairs of lobes on metamorphic shell; (a) dorsal view, noting the metamorphic shell and post-metamorphic shell bounded by the halo (arrow); (f) lateral view; (g) lateral dorsal view. b protegulum and two pairs of lobes on metamorphic shell of a larger dorsal valve. c, e conjunct juvenile valves; (c) ventral view, noting the protegulum and a pair of lobes on metamorphic shell; (e) enlarged ventral metamorphic shell noting the median sulcus. d protegulum, median sulcus and paired lobes on metamorphic shell of a larger ventral valve. Abbreviations: al, anterior lobe; all, anterolateral lobe; c, shallow cleft; f, pedicle foramen; ff, fine fold; ha, halo; ll, lateral lobe; ms, metamorphic shell; np, nick points; pmm, posteromedian mound; ps, post-metamorphic shell; sp., slope; su, median sulcus. Scale bars: 50 μm