車蠔 (spiny oysters)

Coming back from East Dam, I took bus 94 to get to Sai Kung.  Before taking the minibus 1A to get back to Choi Hung, I stopped by the pier and found someone selling a kind of shellfish that I did not recognise immediately.  

They looked like something between oysters and cultivated scallops common at wet markets. The shells are rather rugged and hard  They had to use a hammer to crack the shells.  The meat was sold at HK$ 150 for a pound.  

I think they could be 車蠔 (spiny oysters, thorny oysters).  Or rock scallops.  I am not quite sure. 

My wife stir-fried them.  The meat is tasty but slightly tougher than the cultivated scallops commonly available from wet markets.