Nope they sure can't!!!!
I was going to guess tunicate. Probably have to have a real mature refugium, fine sand size, & a plankton reactor to keep? Even then still need some exp w/ the location of these creatures as far as current is concerned
Like these guys say, u can't know what is what w/o testing. When u do this long enough you will be able to test less by judging the appearance of the tank. If calcium & Alk are where they need to be, you should have coralline algae starting to grow. Have fun. I like 2 parts & limewater...