What is this ?

Well the biggest misconception I think when it comes to bristle worms is when people get them confused with fireworms. Fireworms are very bad, however a actual bristle worm isn't bad and makes a decent clean up crew as stated above. The difference between them visually difficult to distinguish, but it is very often mistaken identity that I believe gave the bristle worm it's bad reputation. Grated they all are variations of the same family of true worms in the class Polychaeta (poly= many, chaete= bristles) that are known as bristleworms. Bristleworms get their name from the rows of bristles that line the back and\or sides of their body. Some fireworms have hollow bristles that contain toxins, which cause a burning sensation when contacted, hence where the name Fireworms came from.

My suggestion would be watch it and if nothing manages to get eaten by it or bothered by it then it will be harmless cleanup. Otherwise if you have fish that start coming up missing or other various strange occurrences then perhaps this worm could be your culprit but in most cases they are harmless.

 

Sounds like good advice, why wouldn't the gorilla crab eat it though ?

 

Probably couldn't catch it or it wasn't in the diet.

 

FWIW, I currently have 2 types of soft corals in my 55g, and have a fist full of "bristle worms", and don't have any issues with the corals, they are thriving and growing.

 

Maybe flip that question around and ask why WOULD it eat it?

 

Hopefully not a eunicid worm

 

Well it's doesn't seem to mind eating my bloody fish, so it might enjoy eating whatevr this is ? It' appears to be a easy meal ?