The new ichnospecies Sinusichnus seilacheri is described from the Middle Triassic Udelfangen Formation (Lower Muschelkalk, Muschelsandstein) near Trier, Germany. It occurs also in the Jena and Meißner formations (Lower and Upper Muschelkalk, respectively) from Thuringia, Germany. S. seilacheri is a horizontal, slightly winding, sinusoidal burrow with T- and Y-shaped branching, sub-angular, elliptical to circular cross section, and a bilobate burrow floor with perpendicular or oblique striations. These features support an interpretation of S. seilacheri as the burrow of isopod crustaceans, while the type ichnospecies of the ichnogenus Sinusichnus, S. sinuosus, is believed to result from the activity of decapod crustaceans. These contrasting tracemakers are an example of behavioral convergence, a fact that helps explain the extended stratigraphical range of Sinusichnus to the Middle Triassic, while previous reports of it are from Late Cretaceous to Pliocene strata. In addition to S. seilacheri, S. sinuosus is reported from the Middle Triassic of Germany for the first time.