What is this goby?

[setanta]

Maybe its not even a goby.
It has a similar shape to the diagonal shrimp goby - but it has a white tail with a couple of black spots - yellow side (pectoral?) fins and a purple/black body.
It was going in under a rock and coming out and dumping sand out of its mouth - digging a hole for itself I guess.
Any ideas?

[PeteM]

Maybe its not even a goby.
It has a similar shape to the diagonal shrimp goby - but it has a white tail with a couple of black spots - yellow side (pectoral?) fins and a purple/black body.
It was going in under a rock and coming out and dumping sand out of its mouth - digging a hole for itself I guess.
Any ideas?

Where did you see it?

Goby's tend to be reasonably localised so someone trying to give an id for a fish in the UK is unlikely to be much help if you saw it in Australia

[setanta]

I saw it in Thailand - Koh Tao