Blue velvet nuibranchs only eat flatworms. They are hard to ship and are somewhat delicate. They also only live about 6 months. I put 2 in one of my tanks a couple of months ago. I don't know if they are still alive, but the flatworm population is way down.

I have a yellow coris wrasse in my other tank. I definitely know he eats them because I can see him picking them off the sand. He's just about got them wiped out in that tank. I had treated that tank with Flatworm Exit before putting the coris wrasse in.

Gary