In the movie THE ABYSS directed by James CAMERON, an alien intelligence tries to contact humanity, creating for it a giant pseudopod able to mimic human expressions. It's a rare if not the only good CGI trick about an unknown creature, because this one is said to be made just of a nearly immaterial substance produced from water.
In Nature, there are really some beings having the same general appearence than the ABYSS' pseudopod. One of them can be seen on the famous video site, You tube :
Another specimen filmed in wide ocean can be seen on this video : http://fr.youtube.com/watch?v=TTTbrDCjzvU and one more is showed swimming in the deep sea : http://fr.youtube.com/watch?v=v_PlNlTa0AI&feature=related.*
This marine creature is a Pyrosoma. Someones can reach ten meters as on the second photography below. It's actually a colony of tiny marine critters forming some long chains like their parents the Salps. More surprising, these animals, although very light and nearly translucent, are not closed to the Jellyfishes, but, like their far parents, the Sea squirts, bearing some similarities with the Sponges inhaling the water beneath the siphons, they have more affinities with the Vertebrates, because their like-tadpole larva bears a notochord, a primitive model of the vertebrate colomn.
An other giant animal, a giant worm, brought a lot of comments : http://fr.youtube.com/watch?v=wST01hAmbRA
This one is undoubtfullly a Nemertan or Ribbon worm, the most primitive animal with a complete tractus ( unlike sea anemons, Jellyfishes and the Flatworms having a single orifice serving both to eat and to expulse ). The not identified creature looks like to some Nemertans like Cerebratulus ( below ). Some Ribbon worms are very long : Lineus longissimus is very thin but has a length of 30 meters, so than the biggest blue Whales ( second photography below ).
I have a bit pride to be the first to have found on You tube the identity of the strangest animal seen on the videos, a swimming creature between a swimming Duck and a pulsing hearth : http://fr.youtube.com/watch?v=oew73zd914w
At first, I was abused by the colour of the water, thinking it would be soft water. After to think to the problem, I talk to myself it couldn' be anything than a marine Mollusc of Gastropoda class, more or less parent of the colourful Nudibranch, dubbed sea slugs. It's in fact a very distant relative of them, a parent of the Aplysia ( Sea Hare ), called Akera bullata, with its tiny shell below the mantle. Drawings from a scientific paper shows the dance of the creature.