Fig. 3.

Hox expression in mesoderm and periostracum of T. transversa. Double fluorescence in situ hybridization of lab, pb, Hox3, Dfd, and Scr with tropomyosin (Tropo, in green) in late larval stages of T. transversa. (A) The gene lab is expressed in relation to the chaetae sacs, but does not overlap with the tropomyosin-expressing mesoderm. (B–D) The Hox genes pb, Hox3, and Dfd show spatial collinearity along the mantle and pedicle mesoderm. (E) The gene Scr is expressed in the periostracum, the epithelium that forms the shell.