I dunno, genetic evolution really really seems to like the crab form...

all you have to do is look at a shark and a dolphin to know that isn't necessarily true

I always think something jellyfish like would be most likely, if I had to picture something like creatures we know

That's why they made them that way. Possible deniability.

Next you're gonna say the government wouldn't ever intentionally infect 1000000s of thousands of people with a virus and then spend decades studying the untreated ailments of it.

Or bombing their own towns.

Or mowing down with assault machine guns their own population. Or poisoning their own drinking water.