Been pulling these out of my skimmer overflow for the past week. This is about number 4. What are they? Asterina? Good or Bad for the reef? I have LPS & softies.
Those are asterinas. Some people say they're good, others say they're bad. I myself consider them bad as I've read way more stories about them eating healthy corals vs. just sitting harmless in tanks. I've also read stories of people having them in their tanks and leaving them alone for months because they weren't hurting anything, then all of a sudden the asterinas go predatorial and take out corals.
No sign of these things for the last 8 months, all of a sudden, they are here in force!
I think they break apart and reproduce fast. Most of the ones I have found, like this on in the picture, have at least one leg missing or partially missing.