[oboes]

An even more bizarre animal is Dendrogaster, a starfish parasite. Believe it or not, but it's a crustacean.

It grows inside a starfish's body cavity until filling it completely, which explains the strange shape of the parasite.

https://www.australiangeographic.com.au/blogs/creatura-blog/...

[bitwize]

Oh, geez, that reminds me of the Mimics from All You Need Is Kill (the basis of Edge of Tomorrow. In the novel, the Mimics are not the alien invaders themselves, but rather nanomachine colonies sent by the actual aliens that infest and control the bodies of starfish, adapting them to combat use.

[bafe]

If you are interested in parasitic crustaceans,you could have a fun time reading about sacculina and the mysterious Y larva