Mutants die at the late embryonic stage with no gross morphological abnormalities. The tracheae of mutant embryos generally do not become gas-filled. Embryos do move but the movements are very weak: slow localised twitches, usually at the posterior end. Some peristaltic motion is visible in the gut, this is very slow. Occasionally embryos bend their heads but movement of the cephalopharyngeal apparatus is not seen. Pumping of the heart is not seen.