Hemizygous mutant embryos show a "buttonhead"-type appearance. The terminal larval cuticle shows defects in head involution and ventral denticle patterning. The fifth-through-seventh abdominal denticle belts are missing or fused.

Ectopic thoracic-like hairs are present anterior to the normal rows of first thoracic dorsal hairs in hemizygous mutant embryos.

Hemizygous mutant embryos show fusion of the labial and thoracic segments with labial tissues developing as first thoracic, yielding an enlarged first thoracic segment. The first thoracic denticle belt appears to form at the labial/maxillary border. The anterior denticle row of the first thoracic segment is directly adjacent to the maxillary cirris in some cases. The denticle belt is frequently split at the ventral midline.

The labial segment does not undergo transformation in hemizygous mutant embryos. Fusion between the labial and first thoracic segment is virtually complete. The dorsal ridge is reduced or absent.

Most of the stomatogastric nervous system is intact in mutant stage 16 embryos, but the corpus cardiacum is absent.

Embryos have a mutant salivary gland phenotype.

First instar larval cuticle shows fusion of the 6th and 7th abdominal segments.

The labial lobe is missing in mutant embryos.

No obvious changes in the expression domains of zygotic hb or Kr. The kni posterior domain extends posteriorly.

Hemizygous embryos lack peripheral nervous system (PNS) structures derived from the anterior compartments of abdominal segments A5-A7, although the peripheral nerve fibres and dorsal cell clusters of A7 are sometimes present. In contrast, posterior compartment PNS structures are largely retained. The lateral chordotonal sense organs of A5-A7 are fused into one or two large clusters and fasciculate with the peripheral fibre of A7.

Abdominal and head defects in the embryo.

Embryos exhibit a gap in their segmentation, abdominal segments 5 to 8 are frequently affected and segments 6 and 7 are always missing.