Another creature...

[Atomic_Mudkip]

To me it looks like some sort of worm? It has like a bristly head that moves occasionally. Should I be concerned?

 

[redfishbluefish]

I only see an out of focused picture of maybe sand in the front with rocks in the back.

Two suggestions....google bristle worms and then try aphasia and see if your hitchhiker looks like one of them.

 

[Atomic_Mudkip]

Sorry it's the white thing on the underside of the rock. My camera isn't great and it's quite small and awkward to take a picture of.

 

[shorty2545]

Hard to tell, but looks like a sponge...

 

[Tahoe61]

If it's a worm it should with draw into the rock work if you shoot some water in that direction. Check out the link below and look for a match. The image is just to grainy and not focused, frustrating I know.

http://www.lionfishlair.com/hitchhikers-guide/