Hi, I am new to this marine lark, and 5 weeks into set up and the number of critters hatching into my tank is fantastic.  However, I have an unidentified invertebrate.  I have a number of 5 and 6 legged brittle star fish, but I also have a Y shaped animal. Photos below- any suggestions?
Thanks

Agree.

Starfish split in half, so you'll notice a lot have some legs longer than the others, whilst they grown new ones.  Eventually they'll all be the same, then that one will split, and the circle repeats.

Thank you for your help 😊