Alpinasub is a company that has a long history of building the spearguns most often encountered in Russia before the arrival of models from companies such as Pelengas (Ukraine). The forward latching design has been used by many companies because there are no pressure boundaries in the gun which are traversed by sliding pins, the trigger pulling an external rod that controls the release mechanism mounted in the muzzle.
The Dolphin gun is a more ambitious design which uses three balls to act as the sear lever, a sliding collar either holds them onto the shank of the piston or withdraws to allow the balls to be pushed outwards thus releasing the piston. When the balls move outwards a sliding bush moves forwards to replace the departed piston tail and keeps the balls from falling out of position. This gun floats after the shot which is a big advantage as years ago such mid-handle guns were always sinkers.