Sea Cucumbers Shoot a Weird, Sticky Organ From Their Butt to Fight Off Predators

Sea cucumbers move slowly down the ocean floor, making them an accessible target for hungry predators. Yet, these large tube creatures rip a hole in the wall of their own butt at the least provocation and spew forth a mess of thin, sticky noodles.

The eviscerated organs of some sea cucumbers, such the black sea cucumber, Holothuria leucospilota, can entangle and neutralize predators. Stress-induced butt-vomiting may seem funny, but it serves a valuable purpose.

A recent study found that the expellable organs, also known as Cuvierian organs, are made of proteins that are similar to those found in spider silk.

The Cuvierian organ, first identified in 1831, is composed of hundreds of tubules that hang from the sea cucumber's respiratory tree (these animals also breath through their butts). Inside the fluid of the sea cucumber's body cavity, their far ends float freely.

The researchers state that a stimulus-selective response in H. leucospilota may only become active when an invading predator applies a considerable amount of physical force directly to the Cuvierian organ.

They followed the molecular chain that sets off the organ's dramatic deployment and discovered that, in contrast to direct pressure, the organ was only faintly triggered by touching or pricking the animal's skin.

According to genetic study, the membranes of the tubules are composed of lengthy, repetitive sequences of amino acids, much like those in spider webs or silkworm threads. While their repetitive nature is well known, the proteins themselves and their configurations are distinctive, and they are what give the organ its great tensile strength.

Due to water rushing through them from the sea cucumber's respiratory tree, the jumble of tubules suddenly swells up to 20 times its initial length within seconds of hitting the ocean. The tubules instantaneously become sticky when they come into contact with any surface. They then cling obstinately to anyone who touches them, like a crab, and entangle them, occasionally killing the offender.

The Cuvierian organ's outer membrane proteins were likewise discovered to contain amyloid-like patterns by the researchers. Known for their role in Alzheimer's disease in humans, amyloid proteins are also employed as a powerful adhesive by other marine creatures like barnacles. Chen and associates speculate that this may also be their function within the Cuvier organs.

Marine scientist Ting Chen and colleagues from the South Sea Institute of Oceanology state in their research, "Our work provides the first genetic insights into defensive ensnarement in a representative species of [sea cucumber]."

In a process known as autotomy, the sea cucumber may self-amputate its Cuvierian organ after being evacuated, much like a lizard shedding its tail. Black sea cucumbers may entirely rebuild their viscera in as little as 15 days, making them ready for the next predator that dared to bother them.

Sea cucumbers are frequently seen partially hidden behind boulders, coral, or clumps of seaweed, thus it is likely that they are hiding once they are safe from assault and have crawled away from the dangerous mess they have caused. They do this by removing organic material from the sand and excreting recycled nutrients like calcium into the ocean, where corals and other creatures may eat them.

Also, according to a genetic study done as part of the inquiry, sea urchins and sea cucumbers split off around 537 million years ago.

But when your butt can instantly channel Spiderman, who needs a coat of spikes?

This research was published in PNAS.