Mutant embryos show detachment of somatic muscles from the extracellular matrix. The mutant embryos show strong defects in midgut development.

A significant fraction of embryos hatch to first instar larvae. Larvae slowly become less motile and die over the next 48 hours. Embryos that fail to hatch exhibit normal muscle attachment and sarcomeric structure, but exhibit defects in the gut. Midgut fails to elongate and only two fat gastric caecae are formed. There is some detachment of the visceral muscle layer, sarcomeric structure is normal. The circular visceral muscles are found as two plates of muscles that are almost completely separated, the longitudinal muscles are also disordered. Hatched larvae exhibit wild type muscles and abnormal midguts. Larval lethality is assumed to result in their inability to feed. Mitotic clones in the wing produce bubbles. 89% of double heterozygotes with mys^xR04 survive.