snoozin

Thanks guys, Are the larger ones any good to eat or just throw them back?

The other weekend I was out along Outer Harbour along the section bank and caught a few of these little critters, they are about 10cm long x 5cm wide on the body, they are a greenish/yellow colour and seem to have sea grass sprouting from their shell. They look like they belong in rocky outcrop locations yet I was in the middle of a large sandy area targeting sand crabs. Does anyone know what they are? Do they grow bigger? and are they common in this area? I have never seen them before.