First thing to note: These little critters are good guys! If you see them in your tank, leave them there.
So, you’ve spotted some legs poking out of your rockwork, that look a bit like worms. They could be plain in colour or striped. Chances are, you are looking at a Mini Brittle Starfish, also known as Baby Brittle Stars.
Mini Brittle Starts are great sandsifters, harmless detritus eaters & in my opinion, fascinating to watch.
If you are just starting to see these critters, it is a good sign that your tank is maturing. They seem to bloom initially, but will eventually control their own numbers once your tank has a bit of age to it & isn’t so nutrient rich.
But, while they are harmless, not everyone wants to see them all over their tank.
How do you control the numbers?
Firstly, you should reduce the amount you are feeding, particularly if you are feeding coral powders. This will significantly reduce the amount of food available to the population. .
Another option is manual removal. You can simply scrape them off of the glass or any other part of the aquarium you don’t want them on.
Do they have any predators?
Please do your research before putting anything new in your tank. But you could look at the following for population control:
A Court Jester Goby may help reduce numbers, they are actually not a goby but that’s its name, these things are very active eaters and will likely help with population control.
Maybe a Harlequin shrimp, their diet is strictly starfish, but there is no real solid evidence that they will predate on mini stars.
Otherwise you could try a Bumble bee shrimp or two!