Found these worm type critters in my substrate during water change. The body is long and slender with a dark colored stripe on it’s back. Has anyone had these and can identify what they are and if harmful to corals, fish or inverts? Thanks.
Looks like baby bristle worms and most class them as beneficial cuc members,I've found a few small ones like yours in my tank .
Aslong as they stay small I don't mind them,but if they get big beasts like 6 inch plus then I don't like them and don't want in my tank ha ha