Mutant embryos have reduced or absent longitudinal connectives and the tritocerebral commissure fails to form. lab²/lab⁹ embryos raised at the restrictive temperature (for lab²) show a loss of the tritocerebral commissure and thinning of the longitudinal connectives. These embryos do not show a mutant brain phenotype when raised at the permissive temperature. When raised at the restrictive temperature, except for 1 hour at the permissive temperature at embryonic stage 11, these embryos show complete rescue of the brain phenotype.

No salivary gland defects.

Hemizygous animals die at the embryonic/first larval instar border. A variable cuticle phenotype is seen, with the severity of the defects correlating with the degree of failure of head involution. The frontal sac appears collapsed, and the pharynx occupies a more anterior position than normal. The salivary glands are missing.