What is this?

[kwan]

I found a number of these under a rock. It is about 5mm long. I had to use a tweezer to remove them as they are attached quite hard. The photos show the top and underside of it. Are they good or bad?

 

[steve-s]

A harmless Chiton...

Cheers
Steve

 

[kwan]

Steve, what do they feed on?

 

[steve-s]

Algae.. 8)

Cheers
Steve