Interesting Aquatic Blob-Creatures

This... is the Pig Butt Worm

Also known as the flying buttocks, Chaetopterus Pugaporcinus's Latin name roughly translates to "Resembling a pig's rear". About two centimeters in diameter, it merrily goes about life around a kilometer under water, where the oxygen is thinner than either above or below. They can't swim, and have no appendages, so they simply eat whatever happens to drift into their mouths.

No one is quite sure what the Pig Butt worm is

It's know that Pig Butt worms are related to tube worms, but no one is sure if they're adults or not. While their life is very similar to larva of other tube worms, their relatively massive size suggests that they're fully grown. However, no one has the slightest idea how they might reproduce.

The Boot Lace Worm

Now, this innocuous little strip of goo is actually a contender for longest animal in the world. Boot Lace worms live in shallow tidal waters, hiding under rocks in giant clustered knots, and giving off a neurotoxin laced mucus.

One Single Worm

The longest recorded Boot Lace worm, or Lineus Longissimus was a whopping 180 feet in length, making it longer than other contenders like the Portuguese Man-o-war, the Lion's Mane Jellyfish, and the Praya Dubia. However, as the worm in question was both stretchy, and dead, it's natural length was questionable. Regardless, it easily makes the top five for longest animal in the world.

The Sea Pig

One of the most boring blobs in the ocean. The Sea Pig is a deep sea sea cucumber, about six inches long. It uses water to inflate sacs in its body to help flex its abnormally large tube feet and walk across the ocean floor, about three to five kilometers under water. They spend their life picking up mud, eating the interesting bits, and spitting the rest out.

A fishy, porcine herd

Sea Pigs have a strong sense of smell, and will head towards more organic mud, congregating in herds towards whale falls and other sources of organic matter.

Going deeper. Getting Simpler

The above image is the "Test" or extruded shell of a Xenophyophore. Some species can grow as large as 20 centimeters across, the size of a small dinner plate. While that might make them only the second largest animal in this list, what they are, is the single, largest CELL in this list. These massive, amoeba like creatures, are single-celled organisms, that build a test around themselves, living in the center, while smaller creatures will often colonize the periphery.

Even Deeper

Xenophyophores are found everywhere on the ocean floor. Everywhere. Xenophyophores up to 10 cm across were found in Challenger Deep, the bottom of the Mariana Trench, the deepest point of the ocean, at 11 kilometers under the water.
Originally believed to be a type of sponge, they take interesting minerals that they find while searching through the muck, and use them to build a shell. Most similar creatures create Calcium Carbonate, but the high pressure of the deep ocean means that Xenophyophores use minerals such as lead and uranium.

The Immortal Jellyfish

Above is the polyp, or juvenile stage of Turritopsis Dohrnii. Bizarrely, though, the polyp may possibly be older than the fully grown, 4 cm long jellyfish shown below.

A True Life Cycle

The Immortal Jellyfish is just that. Immortal. Able to reproduce normally, it also has the fascinating trick of being able to revert to a polyp, which can then anchor itself, grow, and start budding off new T. Dorhnii, making it functionally immortal, never dying from natural causes.

I'm not a marine biologist, this is all the result of quick, second hand research. I just find the variety of life in the oceans fascinating, and want to share these bizarre, amazing creatures with others. I didn't think any of these five were interesting enough to have a post all to themselves, but together, they all share the theme of being weird, obscure, and squishy.

Other interesting deep sea creatures.
The Praya Dubia, contender for the longest living creature: http://imgur.com/gallery/Levro
The Giant Isopod, a really big bug: http://imgur.com/gallery/wsqZi
The Tongue-Eating Louse, a bizarre parasite: http://imgur.com/gallery/2CI8C
The Pistol Shrimp, which uses Hadouken for hunting: http://imgur.com/gallery/NwGb9