Fig. 1

Phylogenetic position of Brachiopoda (A, based on Laumer et al. [58]), metamorphosis of Terebratalia transversa (B, based on Freeman [68]) and detailed morphology of competent larva (C, based on Santagata [70]). S stands for Spiralia, L for Lophophorata. 1 Competent planktonic larva, anterior to the right; 2 Larva settles on the substrate; 3 Inversion of the mantle lobe in the settled larva; 4 Juvenile; note that over the course of metamorphosis the internal surface of the larval mantle lobe becomes external, shell-covered surface of juvenile animal, external surface of the mantle lobe becomes inner surface of the mantle, whereas anterior lobe contributes to the lophophore rudiment developing inside mantle cavity. Musculature in C is depicted in green, nervous system in red and excretory organs in orange. al larval anterior lobe, an anterior nerves, anr anterior nerve ring, cm circular muscle, crs chaetal sac retractor muscle, csm chaetal sac musculature, csn chaetal sac nerve, ds dorsal shell, lgm longitudinal gut-related muscles, lpm lateral pedicle muscle, lr lophophore rudiment, m mantle, ml larval mantle lobe, mo mouth, mpm medial pedicle muscle, np neuropil, nr nephridium rudiment, pcn paraxial nerve cord, pe pedicle, pl larval pedicle lobe, pne pedicle nerve, vmm ventral mantle lobe lateral muscle, vs ventral shell