Perna canaliculus  The green or green lip mussel is farmed and imported from New Zealand.  It is bigger meatier and generally more expensive than the blue mussel.  The green lip often have gapes meaning the shell has a tendency to open.  Because this is a sign of a dead mussel to most chefs, shrinkage tendencies may be higher. To check the mussel tap the shell against a hard surface like a counter top and see if it closes