Isn't this thing super cool looking? This is called a sea gooseberry, or scientifically Pleurobrachia pileus. But lets just say the sea gooseberry. Many divers along the Norwegian coast come across these gooseberries. They float near the surface, and on night dives they can be spotted with just a flash light. Commonly they are found in rock pools and low tides. Can you imagine just flashing your light into the sea and seeing that?! So crazy. They are easily overlooked though because they are only 2.5 cm in diameter. They have two tentacles that can reach as much as 20 times their body length. Cool thing also about thier tentacles is that they can be retracted into pockets inside its body. They flash the rainbow colors because they retract light, and they are really pretty because of that. The rhythmic beating of the cilia allow them to swim. Some sea gooseberries will even eat each other for food. But they also eat fish eggs and larvae, molluscs, and copepod crustaceans. They catch their pray with their long tentacles, which they then real in to their mouth.
I found this REALLY cool video of the sea gooseberry and its movement. Man what an amazing creature!
http://www.arkive.org/sea-gooseberry/pleurobrachia-pileus/range-and-habitat.html