The original 1960s manga is about aliens from mercury invading earth and humanity getting it's ass kicked so badly that we start hiding out in submarines and underwater bases. This cover from one of the original volumes suggests that mutio is in it.
There was also a really short manga based on the ova that was released with the dvds in the Japan.
Couldn't find it on share which is strange because the 1960s one is supposed to be a classic and I've found stuff from the 60s on share before. Sooo... I dunno. There's a doujin of mutio on rapidsearh.yi.org
if you search for mutio.