Nice concept, needs more work.

Your lines are not precise enough, the snake's tail for instance, also it's a little jaggy in places.
The colored outlines are weird, they're too close to the background value to be effective. If you keep this bg, make them  either darker or white; or else make the bg darker or brighter.

The seahorse doesn't really look like one. Also some other animals: turtle, clams.

Then you need to make the seahorse more different to be immediately identified to the player.