There are no syntype specimens known. Warren et al. (1994) examined specimens said to be "Rasmussen's private collection from type locality" and give a "type locality" of Vellerup Vig, Isefjord, 55°44'N 11 °52'E (55.733, 11.8667), 0.5 m. How they obtained the lat/long is unstated, but it is a location inside Vellerup Vig.
Warren, L.M.; Hutchings, P.A.; Doyle, S. (1994). A revision of the genus Mediomastus Hartman, 1944 (Polychaeta: Capitellidae). Records of the Australian Museum. 46(3): 227-256. available online athttp://dx.doi.org/10.3853/j.0067-1975.46.1994.6