The leech moves by producing dorsoventral undulations. Ubx also represses Wingless in the posterior compartment of the dorsoventral axis. Body is oval in cross-section and with some dorsoventral compression. The buccal opening was small and extended in the dorsoventral direction. Wnt signaling is implicated in the formation of the anteroposterior and dorsoventral (DV) axes. According to the dorsoventral inversion hypothesis, an ancestral deuterostome turned on its back. The basis capituli moves in the dorsoventral plane, and articulates with the body proper. It is anteroposteriorly compressed with the dorsoventral diameter longer than the anteroposterior one. The axes include the anteroposterior axis, dorsoventral axis, and right-left axis. Like the Hox genes, "vnd" is required for specification along the dorsoventral axis. Dorsoventral patterning is mediated by Wnt7a signals in the overlying ectoderm not the mesoderm.