Can someone tell me if this normal for a Trochus Snail? I have about 15 of them and two of them have these "tentacles" that are coming from the outer shell. Both of these two snails have a hole or crack in the shell as all others seem pretty solid. When I grabbed them for inspection they retract as does the snail. They re-emerge as the snail does. Wasn't sure if it's actually the snail, or pest. Thanks!