Hi does anyone have an ideas as to what this is? The two antennae are actually part of the critter itself, whereas the rest of the spiral-structure is the “home” it builds (which is quite hard / like a shell — about 1cm diameter).
obv my first concern is whether they’re harmful or just unsightly (one did grow on a Montipora so I’m gonna call that “partially harmful”). So far the only others have built “shells” directly on the rock. Pretty sure they aren’t feather dusters since there’s no fan. Just a gross little white worm with those ugly horror-movie-esque pincer/antennae).
thanks very much for any ideas!