Severe muscle phenotype: myoblasts retain a segmentally repeated pattern but fail to form elongated fibres and establish or maintain their insertion in the epidermis. In less severe cases myoblasts fuse and muscle fibres elongate but fail to reach the right attachment sites on the epidermis. Defects in head and tail structures. Salivary glands of mutant larva escapers exhibit gross morphological defects.

Recessive lethal with a melanotic tumour phenotype as for mod^L4, rescuable with P{mod⁺Sph}, and a dominant suppressor of variegation at In(1)w^m4, as for mod^5.1.