Intestine worm and hairy worm. Also a... mantis shrimp swarm?

[Tired]

I'm pretty sure the smaller ones are bobbit worms, but what is this? It looks like an intestine (or a couple of them twined together, I'm not 100% sure it's only one worm), but it's moving outside of a body, which is pretty uncharacteristic of intestines. It's kind of just curling around in a mess of itself, I'm not sure if it's been damaged somehow. 

I found two of these little hairy creatures. They're wiggly, but pretty slow-moving. 

 

And then there's these. They're maybe 4mm long, so I can't get a better pic. The arrow is pointing at the head end. The limbs near its tail end move like swimmerets, and I swear those limbs at the head end look like mantis arms. There's maybe half a dozen of these in the tank. Is it possible they're super tiny mantis shrimp, little babies? Or are they more likely to be amphipods? They crawl around on the rockwork, and swim now and then, and they don't seem to be afraid of the light. 

[Tamberav]

Baby mantis shrimp kill each other.  

 

Can't tell by the pic...maybe a skeleton shrimp but probably just amphipods.

[Tired]

I don't think I can get a better pic of the shrimp-shaped ones, they're very small. Skeleton shrimp usually grasp at one end and wave in the water column, right? Because these just crawl around. 

 

Another intestine-style worm is emerging from a hole. Any ideas? Its head just looks rounded off at the end.

[Tamberav]

Look up peanut worm

[Tired]

Peanut worms are smooth. This is visibly segmented. 

I had a look here, http://chucksaddiction.thefishestate.net/hitchworms.html and it looks like the one with all the long 'legs' might be syllidae, and the intestine-style one might be an oenonid. The former eats an assortment of sedentary organisms and algae, the latter preys on clams and snails sometimes, so I think I want them out.