It really doesn't seem that much like a virus… just some sort of sea-spider that likes to lay its eggs in other things.
I mean I get that it's injecting the host with its own patterns and whatnot to create more viruses, but… well, so?
This thing is actually kind of less frightening than some actual animals, with just the scare factor that people don't like viruses and find them scary because it's something that can hurt you and do terrible things to you without you seeing it. Once you can see it, it's actually less scary.
This doesn't really evoke any sort of body horror or anything. Even the vague scariness of "Well we don't have a fish or cow handy, may as well feed it a D-class" doesn't even really carry much punch since there's not much reason for them to do so. There's no indication that these are the only specimens alive or that they're even that difficult to come by, so if important research is being done on them (which isn't mentioned even in passing), they could just as easily be allowed to go hungry or die off and then the collection team could go out and get some more. Well, I guess it depends on how these particular researchers view D-class, but since there's no mention of collecting the specimens being particularly difficult or dangerous, that D-class could probably be better used for something else and the collection team could just go swimming again.