Expression patterns of dpp in the trochophore and veliger stages. Expression patterns of dpp in (A, E, I) the trochophore and (B–D, F-H, J-L) veliger stages of the pond snail Lymnaea stagnalis, which has a coiled shell (A-D) dextral strain; (E-H) sinistral strain) and (I-L) the limpet Patella vulgata. (A, E, I) Shell gland (dorsal) view; (B, F) anterior view; (C, G, J, K) left side view; (D, H) right side view; (K) posterior view. (A, E, I) Broken black lines indicate the shell gland, and arrowheads indicate the dpp expression. (A-D, F-H, J-K) Black lines indicate the shell. (A–H) Expression of dpp is asymmetric in the shell gland or mantle edge in late trochophore and mid-veliger sages. (I, K, L) Expression of dpp is symmetric in late trochophore and mid-veliger stages. (J) dpp is expressed in the operculum gland. An, anterior; ap, apical plate; d, dorsal; e, eye; f, foot; L, left; m, mouth; me, mantle edge; op, operculum; P, posterior; Pt, prototroch; R, right; sh, shell; shg, shell gland opening; V, ventral; ve, velum.