Atlantean

Somewhere in deep space, a lone hero detects signals from a distant planet, a planet whose lands were submerged under vast oceans centuries ago. That planet is Atlantis, and it has come under threat by a race of evil machines - the Aquanoids! Their desire is to mutate the peaceful Atlanteans into ghastly bio-mechanical hybrids. The fate of Atlantis now rests on one brave warrior.

Atlantean is a fast action horizontal shoot 'em up in the style of Defender and features:
Arcade quality action
Full chip generated soundtrack
Four epic underwater worlds
Stunning parallax scrolling
Endurance mode
Bonus levels
Impressive bosses to battle