What appears to be the bull's-eye at the center of the butthole is where the creature's mouth is located. In order to feed, said mouth is surrounded by a "cloud of mucus" that catches organic detritus known as marine snow. As far as their appearance goes, researchers at the aquarium offered up this explanation:

"... researchers found that although the worms had segmented bodies, one of their middle segments was inflated like a balloon, giving the animals a distinctive gumball shape. All the other segments were compressed up against the front and back of the inflated segment, like a cartoon character whose nose and hind parts have been flattened in an unfortunate accident."

Karen Osborn/MBARI
Or "ass-ident," as it were.

Rather than reacting with flustered embarrassment, Dr. Karen Osborn of the Monterey Bay Aquarium Research Institute was positively giddy at finding this seagoing sphincter clenching for survival in the bottom of the bay. Most similar worms confine themselves to the mud of the ocean floor, but researchers believe that the pigbutt worm is the first yet discovered to take the "evolutionary leap" of living freely and proudly in the open water. Shine on, you crazy evolutionary abomination.

Wow. OK.

So, males of different animal species use ploys like expansive antler racks and outrageous plumage to attract the opposite sex, but sometimes the females get adaptations for courtship display as well. Female Celebes crested macaques (Macaca nigra) seem to have developed a feature that cuts to the chase. They exploit an anatomical area that humans have only recently begun to celebrate with the advent of Sir Mix-A-Lot's discography.

AP
Cracked Fact: Sir Mix-A-Lot actually received his knighthood for his work in the field of taxonomy.

There are a number of primates that boast unusually large, colorful posteriors, such as baboons. But for sheer bulbous, horrible, in-your-face assy-ness, crested macaques are without rival. Found only on two islands in Indonesia, these monkeys are often mistaken for apes due to the apparent lack of a tail. They do indeed have tails -- it's just hard to tell with so much other stuff going on.

Tony Northrup
"Just once I'd like a scientist to study me for my personality."

There is no specific breeding period for crested macaques. It's backdoor busy season year-round, and the abundant, overinflated, zeppelin-like keisters mean the owners are primed and ready for boarding. Their lifestyle is described as "polygynandrous," a biological term that shares the plot of Pizza Man Gang Bang V: The Pepperoni-ing.

Yes, both male and female crested macaques enjoy multiple sex partners, and the dirty deed is initiated when the female presents her grotesque balloon genitals to the male. Like so:

Even with all that rampant monkey boning going on, Celebes crested macaques are critically endangered due to habitat loss and bush meat hunting, but can you really call it hunting with a target like that?

Daran Kandasamy
Half monkey, half alien dog from Half-Life.

Conservation efforts are being put in place, and fortunately the macaque population has stabilized. And as long as humans stay out of their way, repopulating shouldn't be a problem for these monkeys at all.

Brazilian engineers discovered this creature while draining a hydroelectric dam in 2011, whereupon many reports declared it to be a brand new species. But science has known about Floppy for decades, since the animal was first described in 1968. Biologists aren't exactly sure how this animal breathes, but a group of Brazilian researchers believe that its fleshy wrinkles facilitate skin respiration.

Juliano Tupan
There's hundreds of animators in Japan furiously drawing this as we speak.

And in Asia, we have Urechis unicinctus, a species of marine spoon worm usually found throbbing around the western North Pacific Ocean. Although members from the genus Urechis are sometimes called "fat innkeeper worms" -- as they share their tunnel homes with a variety of other species -- this animal's also nicknamed the sea penis. Here's a video of some sultry Urechis action:

In regions of China, Japan, and Korea, this species is considered a delicacy, and you can find vats of them pulsating at seafood markets. Melt before this creature's Dance of the Seven Veils:

And here it is again, gyrating at some unaroused octopuses:

Because anything that even looks remotely like a penis must logically therefore somehow improve your sex life, marine spoon worms are regarded as an aphrodisiac. In Korea, they're occasionally served alive, sliced up, and writhing, as nothing improves the mood like a confused invertebrate dong that's semi-aware it's on the verge of death.

The turtles aren't normally this pale. Rare albino turtles like these just so happen to occupy a special place in Chinese culture, namely as a mystical creature in the ancient novel Journey to the West. (And no, they're not portrayed as sea monsters with three uncircumcised micropenises.)

scienceblogs.com/deepseanews
"This beast can only be slain with the Jade Dagger of Exiled Foreskin!" -- Something nobody says in Journey to the West.

Also, these turtles have one particular trait that's unique among all other animals. Last year, biologists at the National University of Singapore reported that an unusual gill-like structure in the turtles' buccopharyngeal region is actually being used to expel urea. Indeed, Chinese softshell turtles piss out of their mouths. At least evolution's keeping things thematic.

Bearded sakis also engage in geophagy, meaning they like to eat dirt. This is an unusual trait for primates. But -- running in contrast to their lamentable reputation as butt-monkey hybrids -- this behavior is thought to merely supplement mineral intake and soothe gastrointestinal problems like diarrhea. So at least bearded sakis are making an effort not to be totally gross.

Ana Cotta
Nonetheless, their profiles alone are an FCC violation.

Let's get one thing out of the way right now: This isn't just us saying, "Hey that sort of looks like a bird poop." These creatures actually evolved to look like turds, because, duh, most predators don't want to eat s**t.

Thomas Ziegler
"I thought you ate pieces of s**t like me for breakfast? Yeah, that's right, just walk away ..."

For instance, in another article, we told you about the spider that hides from predators by doing a spot-on impersonation of bird dook. Well, mimicking a fresh-squeezed growler is a viable survival strategy all across the animal kingdom. Behold the caterpillar of the giant swallowtail butterfly (Papilio cresphontes).

Bob Harris
"Wait till those other turds see me at the 10-day reunion."

The giant swallowtail is the largest butterfly in North America. Before it takes to the air, it has to spend some time camouflaged as bird crap. But hiding out as avian droppings isn't the only trick up its sleeve. When pestered, they flick out a bright red Y-shaped organ called an osmeterium from behind their head. (Here it is in action.) In addition to emitting a foul smell, this contraption looks enough like a snake tongue to scare off potential attackers, even those desperate enough to eat a piece of crap.

PicsWeb
"Please don't eat me. I have a wife and three snake-poop daughters."

And it's not just insects that are into the doo-doo double-cross. Climbing a few rungs up the evolutionary ladder, we find a Southeast Asian amphibian known as the pied warty frog (Theloderma asperum). It's also called the "bird poop" frog, for obvious reasons, but it's not the only frog to have been saddled with that distinction. It is, however, probably the most deserving.

generalexotics.com
We'd say not to judge him on looks, but his personality is pretty crappy, too.

The gambit is apparently paying off, because this frog is hardly ever seen in the wild. Maybe people are actually seeing these things all the time and are simply not the type of folks to meticulously examine every stray wad of bird glop.

kin_onn
Congratulations, you found me! Also, what's wrong with you?

E. Reid Ross writes some other stuff at RealToyGun.com.

For more reasons Mother Nature seems like a cruel prankster, check out 8 Terrifying Skeletons of Adorable Animals and 5 Lovable Animals You Didn't Know Are Secretly Terrifying.

If you're pressed for time and just looking for a quick fix, then check out The 3 Most Terrifying Faces Drawn by Nature.