#2
I know of no other species with this feature. There is no species like this in Disney (1975) for the british species, and in Tsalolikhin (ed., 1999) this seems to be the only species with this feature. Note that not all Dixella have been described in the larval stage (as far as I can tell), but the basal plate looks very much like D. luctuosa.
By the way, Fauna Europea says that D. nigra (Staeger) is the true name.