May be involved in shell and shell gland formation during development. Expressed in the dorsal ectoderm of early gastrulae in a band corresponding to the peripheral area of the presumptive shell gland. Also expressed at four points along the posterior ectoderm. In late gastrulae, it is predominantly expressed in the peripheral ectoderm of the shell gland and in spots at the posterior end behind the presumptive foot. Expressed in late trochophore larvae at four points behind the foot, at two locations at the base of the foot and in the peripheral ectoderm of the shell gland. Expressed during embryonic development in the early and late gastrula stages, but not in the gastrulating blastula stage. Also expressed in the late trochophore stage. Belongs to the engrailed homeobox family.