4-5" black & white striped. Looks like an eel, but may not be. Fairly inexpensive (less than $10/per). Saltwater, reef safe. I will try to post pics later.
I believe engineer gobies can grow to about a foot
And they like digging tunnels in the sand, so make sure the rocks is on the glass, otherwise it might collapse
engineer gobies do get long,i was over at rstimeout's house and when he fed the fish i asked"what kind of eel is that?":smash: he said those are his engineers:duh: .