Rattails are the most abundant species found living just above the bottom of the sea floor. They have big heads and thin tails. They swim slowly with their heads angled down into the current looking for food.
Umbrella octopuses have a web of skin between the tentacles. They swim up above the ocean floor, spread their tentacles looking like an opened umbrella and collect food as they float down.
The helmet jelly is found in every ocean of the world except the Arctic at depths as deep as 7000 meters. They are 90% water and the rest is tissue and a gelatinous mass. They light themselves from within with bioluminescence.
Acorn worms have no bones, no eyes and no brains with soft and gelatinous bodies. They crawl over the surface of the mud slurping the sediment and excreting a trail behind them.