Not even tardidgrades are invulnerable

They may be cute and cuddly, but even tardigrades have problems.

It is also called the water bear as it resembles a kind of adorable multi-legged furless teddy bear that you can’t really hug because it is too small. The tardigrade has a strong defence against most life threatening circumstances it encounters (dehydrating and dying for a while until conditions improve), but this almost invincible micro-beast is not so resistant to certain types of threats. Like every other living thing, this little creature can fall victim to merciless parasites.

A while after establishing contact with the water bear, the fungus begins its takeover. The tardigrade's cuticle is still a barrier, but the fungus has a way of bypassing that. The spore develops what is called a ‘germ tube’, a long outgrowth that penetrates into the tardigrade's body.

After the germ tube is inserted into the body, the fungus starts to grow what looks like branches all through the inside of the tardigrade. It continues to spread as it feeds; the branches taking up all the room inside, squishing and crushing the animalcule's organs, and it eventually kills the tardigrade. However, some the branches becomes abjointed and will drift within the body of the host becoming much like a harmless floating husk. This continues until the water bear's organs fail, but now that the host is dead, asexual reproduction can take place!

http://dailyparasite.blogspot.com/2014/08/ballocephala-sphaerospora.html