New hitch hiker

[Delilah]

Hi
Would anyone be able to tell me what this tiny hitchhiker is?

 

[Tyko_N]

Looks like an Asterina starfish, probably harmless but some are said to eat corals so it might be worth keeping an eye on it.

 

[Tanksy]

Some Asterinas (like the one you have) are harmless algae eaters, others will eat certain corals (zoas, organ pipes & candy canes).
All Asterina species can reproduce very quickly and plague a tank to unsightly proportions, that's why almost all hobbyists consider them a pest.

 

[malik uddin]

you should get rid of it