VL1 muscles begin to exhibit an abnormal teardrop shape at stage 13 in mutant embryos, ending in thin projections oriented toward the appropriate tendon cells, instead of having a wide rectangular surface of attachment as occurs in wild-type embryos. As development proceeds, the VL1 muscles become more dysmorphic, assuming rounded and irregular shapes. Occasionally, at later stages, random projections originating from the mutant myotubes are seen.

At stages 13-14, approximately 60% of muscles have abnormal projections and approximately 40% are wild type in mutant embryos. At stage 15, a small fraction of muscles with misdirected projections are seen, as well as most muscles having abnormal projections. At stage 16, less than 20% of muscles are wild type, approximately 60% have abnormal projections, and more than 20% are rounded.