Thats exactly what should be checked for, those are strings from vermetidae snails. They are a pest, but bumblebee snails have a chance to eradicate them, but its hit or miss on it. If there is not a huge infestation, try and find them and break them off the rocks and throw it away.
sometimes they are so small and inside a crevasse you can't tell, you just start digging in the area. Other times they are small brown balls with a tiny tube especially when young, I have seen some the size of a BB and some the size of a ball point pen tip.
you seem more correct, I didn't notice the pattern on the tentacle until you said something.
Can I have those in a 5g?
Thanks!
How old is your tank? They might go away on their own...
A tuxedo urchin? Maybe, but you’d probably be pushing it. Small hermit(s)? Probably. Starfish? Only Asterinas (technically Aqulionastra stars, but known in the hobby as Asterinas) - the rest need way more space. Some people consider the Asterinas pests because of how fast they reproduce though, and I’d imagine they could get out of hand really fast in a 5 gallon.
Yes
Like 1.5 years
