This is a short but stunning video of a rarely-seen fish, the fanfin anglerfish Caulophryne jordani, one of 160 species of deep-sea anglerfish.  It shows a bizarre female with her huge mouth and onboard lights to attract prey (and mates) in the dark, as well as the tiny male, who, because population density is low, fuses to the female’s body and, losing its head, becomes part of her for life—a parasitic bag of sperm.

You can read more about this video at Science; I’ll give one excerpt:

The video was captured at a depth of 800 meters by deep-sea explorers Kirsten and Joachim Jakobsen in a submersible. The husband and wife team was nearing the end of a grueling 5-hour dive along a steep deep-sea wall on the south side of São Jorge Island, when “something with a funny form” caught their eye, Kirsten Jakobsen says. Aborting their plan to surface, the filmmakers followed the strange creature around for 25 minutes, capturing its movements through the submersible’s 1.4-meter-wide window. It was exciting, but also challenging to maneuver the craft to get the best images because the female was only about 16 centimeters long, she says.

After surfacing, the duo sent the video to Pietsch, who identified the species as Caulophryne jordani, known as the fanfin angler. He was entranced by the species’s “gracefulness,” especially the way those whiskerlike structures—called filaments and fin rays—enveloped the animal. “Any prey item touching one of those would cause the angler to turn and gobble up that particular animal,” he says. “They can’t afford to let a meal go by because there’s so little to eat down there.” The video was captured in August 2016, but this is the first time it’s been released to the public.

C. jordani’s light show was also a stunner. Like other deep-sea anglerfish, the female has a bioluminescent, lurelike appendage that drifts in front of her head to attract prey. But in the video, the filaments and fin rays also appear to emit light at their tips and at intervals along their length—something that’s never been seen before. Pietsch suspects that the light is bioluminescent—meaning, it’s produced within the animal itself—but he notes that it’s hard to know whether the structures are reflecting light from the submersible or are actually glowing.

The tiny male is also a key part of the discovery. Like many other species of anglerfish, C. jordani forms a permanent pair bond—once a male finds a mate, he bites into her, eventually fusing with her tissue and gaining sustenance through her blood stream. Scientists have known about this bizarre reproductive strategy because they’ve seen dead males latched onto dead females, but people have never seen it in the wild—until now.

Bruce Robison, a deep-sea ecologist at the Monterey Bay Aquarium Research Institute in Moss Landing, California, was impressed with how flexible the male was despite its solid attachment, seemingly moving around in any direction he wished. “There’s no way I would have ever guessed that from a [museum] specimen.”

I wonder if more than one male can fuse to a female at once, if she has any say in the process or can’t give affirmative consent, or if she can reject an unsuitable male. Who knows? In some ways the deep sea is as much a mystery, or even more of one, than bodies like Mars and the Moon.

This video, embedded in a report posted by Science, shows the remarkable behavior of the pelican eel (Eurypharynx pelecanoides), also called the “gulper eel” for reasons that will become obvious.  This rarely-seen creature, the only species in the family Eurypharyngidae, has now been put on video for the first time. While Wikipedia says this,

The stomach can stretch and expand to accommodate large meals, although analysis of stomach contents suggests they primarily eat small crustaceans. Despite the great size of the jaws, which occupy about a quarter of the animal’s total length, it has only tiny teeth, which would not be consistent with a regular diet of large fish. The large mouth may be an adaptation to allow the eel to eat a wider variety of prey when food is scarce. It can also be used like a large net. The eel can swim into large groups of shrimp or other crustaceans with its mouth wide open, scooping them up as it goes. The gulper eel is also known to feed on cephalopods (squid) and other small invertebrates. When the eel gulps its prey into its massive jaws, it also takes in a large amount of water, which is then slowly expelled through its gill slits. Gulper eels themselves are preyed upon by lancetfish and other deep sea predators.

. . the video suggests that the creature eats more fish than previously thought. Here’s part of the news piece in Science.

What would you get if you crossed a pelican with an eel? Probably something close to the aptly named pelican eel. . . a bizarre-looking fish with a slender body and a head that inflates like a balloon.

Because the pelican eel prefers to live between 500 and 3000 meters below the surface of tropical and temperate seas, it is seldom seen or photographed by humans. This makes it difficult to study the eel’s behavior to look for clues as to why it evolved such a strange head.

Now, researchers have made what they believe to be the first direct observation of a pelican eel hunting for prey and captured the behavior on video. Researchers piloted a submarine to a depth of 1000 meters in the Atlantic Ocean, about 1500 kilometers off the coast of Portugal near a constellation of islands known as the Azores.

The team spotted the eel not only inflating its head to form a pouch for catching prey, but also actively hunting and swimming after smaller fish. Previous research had hypothesized that the eels inflated their heads to lure their prey or to create a large hole into which food could fall out of the water column, but these studies relied on evidence from the stomach contents of dead eels. The new video evidence suggests the eels take a much more active role in finding food: exploring their surroundings, stalking prey, and inflating their heads to maximize the probability of engulfing them.

Here’s the video of a gulper eel filmed from a submersible off the azores; the video is stunning: