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.
