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Brainless, Eyeless Deep-Sea 'Flatworm' Finally Identified

Four new species of deep-sea animals that look like deflated whoopee cushions and lack complex organs have helped solve a complicated puzzle.

Four new species of deep-sea flatwormlike animals that look like deflated whoopee cushions and lack complex organs have helped solve a complicated puzzle about their group's placement on the tree of life, scientists found.

The new study, representing 12 years of specimen collection and analysis, adds the new species to a group previously known by only a single species, and in doing so, provides a clearer picture of the evolutionary position these animals hold.

Hermaphrodite Worm Has Sex With Its Head

When describing the physical characteristics of these baggy marine creatures, "simple" doesn't begin to do justice to how simple they are, as animals go. They have no recognizable face or limbs. Their bodies are blobs that look more like empty socks than animals, and are wrinkled by muscular folds and propelled by cilia. A mouth opening at one end leads to a gut sack, but there is no anal opening in the back end. They have no digestive system, no excretory system, no reproductive organs, but they probably don't worry about that too much because they don't have brains, either - just a neural network. [Video: New Worm Species Looks Like 'Churro' Fried Dough Pastry]

Surface appearances aside, this genus - Xenoturbella - has proved surprisingly difficult to position on the tree of life, ever since the first species, Xenoturbella bocki, was discovered in 1950, according to the study researchers. Scientists first classified it as a flatworm, and then, in the 1990s, suggested that it was a type of mollusk that had "degenerated," losing its more developed features over time to reach a simpler form. This explanation placed Xenoturbella closer to vertebrates andechinoderms - the group of marine life that includes starfish and sea urchins - rather than in an earlier evolutionary location on a more distant branch from these more complex animals.

NOAA Salutes The Ocean: Photos

But new genetic data, with more than 1,000 genes sequenced from just one of the new species, disproves that Xenoturbellawas once complex, according to study lead author Greg Rouse, a marine biologist with the Scripps Institution of Oceanography, at the University of California at San Diego. "Our new analysis and that of another paper in the same issue of Nature using much more data overturns this idea, and supports the idea that Xenoturbella is simple," Rouse told Live Science in an email. "Sequencing more than 1,000 genes of one of the species gave a large amount of data that could be directly compared with other animals," he said.

The new species - X. hollanduram, X. monstrosa, X. profunda, and X. churro (named after the fried-dough dessert)-were found in diverse and remote deep-sea locations off the coasts of California and Mexico, the deepest of which, where X. produnda hugged the seafloor, was a hydrothermal vent 12,139 feet (3,700 meters) below the surface of the Gulf of California. The biggest species, X. monstrosa, measured 8 inches (20 centimeters) long, while tiny X. hollandorum was a mere 1 inch (2.5 centimeters) in length.

Deep-Sea Worms Can't Take The Heat

Finding four new species "was a surprise," Rouse said, "especially as people regularly visit methane seeps and hydrothermal vents and haven't picked them up before." Rouse added in a statement that these new species likely represent just the beginning of unraveling Xenoturbella‘s biological mysteries, and that he expects to see more discoveries of these animals around the world in the years to come.

The findings were published online Feb. 3 in the journal Nature.

In Photos: Worm Grows Heads and Brains of Other Species Deep-Sea Creepy-Crawlies: Images of Acorn Worms In Photos: Spooky Deep-Sea Creatures Copyright 2016 LiveScience, a Purch company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

Article first appeared on LiveScience.

Shown is the new worm species Xenoturbella.

The National Oceanic and Atmospheric Administration (NOAA) is celebrating "30 Days of the Ocean" in the month of June, and in honor of the organization's hat-tip to life undersea, we take a look, this final June weekend, at some of the organization's captivating marine life snapshots. Here, the eyes of a queen conch (

Strombus gigas

) peek out from under its shell in La Parguera, Puerto Rico.

PHOTOS: 30 Days of the Ocean

Kelp and sardines, just doing what they do, off Anacapa Island, Channel Islands National Marine Sanctuary.

Whales Get Fishing Tips From Peers

This school of permits contains 60-80 individuals, each more than a foot long. The school was observed in the Dry Tortugas, Florida.

PHOTOS: Shipwreck Hunt Turns Up 'Tar Lilies'

A Caribbean spiny lobster strolls on the sea floor. This photo was shot during a 2010 NOAA expedition in the U.S. Virgin Islands to map underwater habitats and the marine life they support.

Deep-Sea Methane Ecosystem Found in Atlantic

DNA testing confirmed that the eggs pictured here were those of a loggerhead turtle, a marine reptile species listed as threatened under the Endangered Species Act. The testing was done by NOAA's Center for Coastal Environmental Health and Biomolecular Research, in Charleston, S.C., the only lab in the country dedicated to forensic analysis of marine species.

PHOTOS: Sea Turtles From Shell to Surf

This manta ray coasts over a reef, in the process inviting much smaller fish to clean parasites and other debris off of it. Manta Rays are the largest type of ray in the ocean.

The World's Biggest Manta Ray Sanctuary Created

Make way for the balloonfish, also known as a porcupine or spiny puffer fish. As its name suggests, it will swell up like a balloon when attacked.

VIDEO: Flushed Fish Invading Oceans

Here we see a close-up of brain coral in the Dry Tortugas, Florida.

Off the California coast, a group of elephant seals sleeps in the sun on a sand dune on Active Point, San Miguel Island, part of the Channel Islands National Marine Sanctuary.

With its distinctive reddish and white stripes, its gracefully flowing fins, and its menacing spine, not many fish can embody the beauty, mystery, and danger of the ocean quite like the lionfish. Although it's native to the Indo-Pacific region, lionfish were introduced to the Atlantic and are now found along the U.S. coast, from North Carolina to Florida, and in the Bahamas and Caribbean. The lionfish spells trouble for the balance of ecosystems and fisheries it invades, as it can out-compete native species for food and space. It lacks predators, has a voracious appetite, reproduces quicly, and is spreading fast.