Flatworm?

[Ahowell]

I noticed this in my tank after receiving an order of Flat Branch Gracilaria and Red Gracilaria. I think it’s a flatworm but have no idea what kind. It has left my corals (softies) alone and I have mostly noticed them on the glass and in the rock work. Anyone know what it is?

 

[rayadog]

It is quite hard to make out; even the general body plan. But based one what it looks like in the pictures and your assumption description, my guess would be something like a sea hare.