When danger calls, some animals bare their teeth. Others take to the sky, or curl into protective balls. But the remora — a fish that often hitches a ride on larger marine animals like sea turtles, whales and sharks — sometimes follows a less dignified strategy: It disappears inside a manta ray’s rear end.

In a study published on Monday in the journal Ecology and Evolution, a team of researchers referred to this newly observed behavior as “cloacal diving.” While many questions about this fishy practice remain, there is one thing the team feels sure about.

“It does not look like the manta ray likes it,” said Catherine Macdonald, director of the shark research and conservation program at the University of Miami and senior author of the new study.

While remoras, also known as suckerfish, have been observed diving into the safety of whale-shark cloacae in the past, this is the first time anyone has documented the behavior in manta rays.

The paper uses seven instances of cloacal diving that took place between 2010 and 2025 across all three known species of manta ray. What’s more, the observations, which were gathered by the Marine Megafauna Foundation, occurred in three separate ocean basins, suggesting that this previously unobserved behavior could be common among rays and the remora species that associate with them.

In some cases, the remora forces itself so far inside the ray’s cloaca that only the very tip of its tail can be seen protruding from the exterior. In others, the ray is not large enough to accommodate the remora’s entire body, and half of the suckerfish hangs out of the ray, like a toddler playing peekaboo beneath a blanket.

“The remoras are pretty much as wide as the cloaca is,” said Emily Yeager, a Ph.D. student at the University of Miami and the lead author of the study. “So it’s fully filling that opening.”

To the researchers’ knowledge, no one has studied how sensitive manta ray cloacae are specifically, though Dr. Macdonald said that her lab would often swab the cloacae of sharks for fecal DNA to better understand what they’d been eating.

“They don’t especially like us sticking a swab up there,” she said. “And that swab is a big Q-Tip compared to a remora.”

While all of this may seem as if it’s a lark — News flash: Fish hides inside another fish’s backside — the findings contribute new information to a topic already hotly debated by scientists: the type of impact remoras have on their hosts.

Traditionally, experts have seen the interaction between remoras and manta rays as either commensal or mutualistic. In a commensal relationship, one animal benefits while the other is neither benefited nor harmed. In a mutualistic relationship, both creatures benefit: The remora gets a free ride and food, while the manta has its skin cleaned of parasites.

But cloacal diving almost certainly changes the equation, said Eleanor Caves, a sensory biologist at Brown University who was not affiliated with the new study. While the remora’s presence inside the ray is most likely brief, it could interfere with waste discharge or reproduction, or even damage the cloaca’s lining. This may mean the relationship between remoras and manta rays sometimes tilts into a parasitic interaction, in which one species benefits and the other is harmed.

While the researchers provide just seven instances of remoras using manta-ray cloacae as their own personal panic rooms, the fact that the animals are so difficult to see once inside suggests that the behavior is under-documented, at the very least.

“It’s really challenging to study these highly mobile relationships in marine systems,” Ms. Yeager said. “Oftentimes when researchers interact with these organisms, it’s just for a second in time, when we’re scuba diving in one location and one passes over us, or we’re fishing in a site and we bring one to our boat.”

“But these relationships persist 24/7, all of the time,” she added. “And we’re seeing just a snapshot.”

Mandy Rosenberg, 35, from Brookfield, Wisc., has always drawn attention because of her looks. With her long blonde hair, athletic build and large blue eyes, she was called Barbie by some of her high school peers.

But even though people often told her that she was pretty, she didn’t view herself the same way.

She’d spend hours staring at a tiny blemish on her forehead that was barely visible to others. In her mind, it was a large and unsightly scar, and she would climb on top of her bathroom sink to get as close to the mirror as possible while examining it.

“If I couldn’t make that go away, I didn’t want to live anymore,” she said.

Ms. Rosenberg didn’t know it at the time, but she had both obsessive-compulsive disorder and body dysmorphic disorder, or B.D.D., a mental health condition that causes people to spend an inordinate amount of time worrying about their appearance — to the point where they may isolate themselves from others and feel imprisoned in their own bodies.

People with B.D.D. not only think they look unattractive but can become convinced that others will reject them because of their flaws.

“They often feel they’re unlovable,” said Dr. Katharine Phillips, an expert in B.D.D. and a psychiatrist at Weill Cornell Medicine and NewYork-Presbyterian.

What is body dysmorphic disorder?

Those with B.D.D. fixate on perceived cosmetic problems that to others appear unnoticeable or minor. But it’s not about vanity; instead, people with B.D.D. feel extreme anguish that impairs their functioning.

The disorder typically emerges during adolescence and is estimated to affect 2 to 3 percent of the general population, but these numbers may be conservative because the disorder is underdiagnosed.

Studies have shown differences in the brains of people with B.D.D., said Dr. Jamie Feusner, a professor of psychiatry at the University of Toronto Temerty Faculty of Medicine. Some of his research has found that in those who have the condition areas of the brain that help us view things holistically are underactive.

This might be part of the reason that people with B.D.D. have trouble viewing their imperfections as small relative to their entire face or body. It’s akin to looking at a window with a smudge on it, then “thinking that the whole window is ruined,” Dr. Feusner said.

Patients with B.D.D. aren’t always aware that their concerns stem from a mental health problem. Instead, they often believe wholeheartedly that they have physical defects.

Because of this, someone might suffer for a decade or more before seeking help from a mental health provider, said Hilary Weingarden, a psychologist in Massachusetts who studies O.C.D. and related conditions.

Instead, “they’re going to their dermatologist and a plastic surgeon and the dentist and the aesthetician,” she said.

But trying to “fix” their appearance only serves to maintain and exacerbate their anxiety in the long run.

What are the signs and symptoms?

People with B.D.D. may withdraw from relationships, avoid attending work or school, and spend an excessive amount of time on repetitive behaviors like examining themselves in the mirror, attempting to camouflage their appearance or seeking reassurance from others.

Chris Trondsen, a therapist in Costa Mesa, Calif., who diagnosed Ms. Rosenberg with B.D.D., said his patients admit to spending hours chatting with artificially intelligent bots, both seeking affirmation and asking what they ought to fix.

“If you ask a human, people are going to get fed up answering the questions,” Mr. Trondsen said.

Mr. Trondsen was inspired to study psychotherapy because of his own struggle with B.D.D. He used to fixate on his complexion and other parts of his body, too. He worried that his nose was too large for his face and that his body wasn’t muscular enough, a form of B.D.D. called muscle dysmorphia.

“I kept thinking I was getting uglier,” Mr. Trondsen said.

Like many patients with B.D.D., he also spent hours checking his body in mirrors and rarely left his apartment. At 21 years old, Mr. Trondsen became so isolated and consumed by his appearance that he attempted suicide, and might have died had his roommate not discovered him. After that, he sought help and was diagnosed with O.C.D. and B.D.D.

It’s common for those with B.D.D. to also have conditions like O.C.D., major depressive disorder, social phobia and substance use disorder. Studies indicate that people with B.D.D. have high rates of suicidal ideation and behavior, too. One meta-analysis found that, across a patient’s life span, about 66 percent of those with B.D.D. will have thoughts of suicide and around 35 percent will attempt it.

How is it treated?

Cognitive behavioral therapy for B.D.D. has been shown to lead to remission in more than half of patients. It includes exposure and response prevention, which is meant to help patients gradually confront the things that they have been avoiding or the rituals they have become dependent upon, like hiding parts of their body with clothing or makeup.

Therapists try to help patients view themselves more holistically, emphasizing that there’s more to them than the specific parts of their bodies they scrutinize.

The disorder can also be treated with serotonin reuptake inhibitors, or S.R.I.s., often at high doses. For those with severe B.D.D., both medication and C.B.T. are recommended, Dr. Phillips said.

For Ms. Rosenberg, cognitive behavioral therapy with her former therapist, Mr. Trondsen, gradually helped her condition.

Later, as part of her treatment, she created a diagram showcasing all of the things that contribute to her identity: She is a daughter and a faithful Christian, she loves dogs and cats, she is a teacher, she is caring — she is more than just her looks.

My body, she said, “doesn’t get to determine how I go about my day.”