Cuttlefish, like their cousin the octopus, have eight arms. Cuttlefish differ however in that they have in internal calcareous "shell" that is porous; they use this for buoyancy control in order to hover level. Their movement is largely controlled by fluttering fins along the side of their body. They also have two specialised tentacles; they can shoot them out to grasp their prey.
Cuttlefish swim and hover using their fluttering side fins, but when they need to make a quick escape they use a water jet below their bodies - you can see these two fighter planes in the photo as they make a quick escape!
The mourning cuttle has a longer body than the giant and red cuttles that you also find in Sydney. The blue lining in the eye and smooth eye sockets are the other indicators of this species.
