What is this?

Alexander

Good evening) Can you tell me what this is? A month ago, I discovered two creatures crawling on the stones, resembling snails but without shells. They have a plate on their backs, and the "snails" were no bigger than a centimeter. After a month, they grew to 3-3.5 cm, crawl very quickly, and I have only seen them on the stones; they don't touch the corals. In general, they behave like snails. I'm curious, are they harmful? And will they stop growing?

Jessica5348

This is indeed a mollusk, specifically a snail. It's called Stomatella. I had quite a few of them in my aquarium, plus some coal-black ones. Don't worry, they are very useful creatures. They feed on detritus and various growths.

Brandon9634

Here -

Susan

Thank you, definitely a stomatella) one is 3 cm, the other is slightly larger, probably a juvenile))