There seems to be some confusion in the question. There is no known animal called a "spaceship snail." It is possible you are thinking of the "sea butterfly."

Sea butterflies are small, planktonic sea snails that swim using wing-like structures. They are not known for speed; rather, they drift with the ocean currents, giving the appearance of "flying" through the sea. These snails are quite fragile.

• Sea butterflies use wing-like parapodia for locomotion. Source
• They are typically found drifting with ocean currents. Source
• They are a type of sea snail known as a thecosome pteropod. Source