A Tbx6-related gene is expressed in cells of the muscle lineage in tailed (urodele) ascidians and is involved in the maintenance of transcriptional activity of muscle-specific structural genes. We describe here the expression pattern of a Tbx6-related gene in the tailless embryo of Molgula tectiformis. Although tailless embryos don't differentiate muscle cells, a Tbx6-related gene was expressed in muscle lineage cells at the gastrula and later stages. These results suggest that the upstream regulatory machinery for the expression of muscle-specific structural genes may be intact, even though there are no longer functional muscle cells in the tailless embryos.