What is this sandworm/caterpillar like creature?

[Kirino]

Anyone know what this little worm thing is? It was on a rock with some sand I got with a Zoanthis frag. It looks like a sand worm, but also a little like a caterpillar when it moves, but it can also dash real quick if it wants. Funny little critters, there were tons of them.

No clue if it's harmful or not, but they kinda all died from the coral dip I used. Rest in piece you poor little critters.

 

[kharmaguru]

Hard to tell but I was thinking they are more crustacean than worm, so some type of copopod/amphipod.

 

[griss]

Hard to tell but I was thinking they are more crustacean than worm, so some type of copopod/amphipod.

My thoughts as well.

 

[Mike Ordner]

My eyes aren't as good as they used to be, but looks like maybe munnid isopods. Good guys, more free fish food.