You are not fascinated by sea cucumbers? Wait until you read this.

Self-disembowelment

When threatened by predators like crabs, some sea cucumbers can forcefully expel their internal organs through their anus. This can include parts of their intestines, respiratory trees and reproductive structures.

It sounds like a high-stakes defence, right? Here is how it works.

The goal is to distract the predator. The expelled organs are often sticky, messy, and sometimes toxic, designed to entangle, confuse, or sicken the predator. This gives the sea cucumber time to escape.

Many species release specialized tubules from their anus. These strands expand rapidly upon contact with seawater, becoming extremely adhesive to trap attackers.

Don’t worry, there is no permanent damage. The act of self-evisceration is not fatal. The sea cucumber can regenerate its lost organs, with full recovery taking anywhere from a few days to several weeks, depending on the species and environmental conditions. Sea cucumbers are masters of regeneration. Their bodies contain special cells that can regrow the entire digestive system.

While some species use this as a defensive last resort, others may also use it to get rid of parasites or simply as a way to shed waste.

Soft & Solid

Sea cucumbers possess the remarkable ability to change their body consistency from rigid to nearly liquid on command. They use this skill to hide in crevices or escape predators. It is controlled by their nervous system, which acts on a unique, flexible material in their skin known as mutable collagenous tissue.

Melting (softening)

When threatened or trying to squeeze into a tight spot, the sea cucumber activates proteins that unlink the collagen fibers in their skin, causing the body to become soft, jelly-like, or almost liquid.

Solidifying (stiffening)

Once they have wedged themselves into a crack, they can instantly trigger a “stiffening protein” that locks the collagen fibers back together, making them rigid and nearly impossible for predators to remove.

This transformation can occur in a matter of minutes or even seconds.

The purpose of this adaptation is either to hide or escape. Or it can act as a defence mechanism. While their skin is usually leathery, this ability to become rigid makes them difficult to bite or digest.

This “shape-shifting” ability is considered a form of “living hydraulics” and has inspired researchers to develop new, flexible, and adaptive materials for robotics and medicine.

Visitor in the anus

Slender Pearlfish often live inside various invertebrates including the anus of sea cucumber. Because a sea cucumber breathes by taking in water through its anus, a pearlfish can wait for the cucumber to open for a breath and swim in.

The relationship between pearlfish and sea cucumber is beneficial to the pearlfish, providing shelter for this slender, scaleless, and often translucent fish. The relationship may be commensal, in which no harm is done to the host sea cucumber, but in some species the pearlfish can function as a parasite, causing harm to its host by eating its gonads and other internal organs!

Pearlfish are most common in tropical shallow-water sea cucumbers, but they have been found in hosts in depths of up to 2000 meters! There may be just one pearlfish to a sea cucumber, but some sea cucumbers may shelter five or more pearlfish. Other animal, including oysters and sea stars, can also play host to pearl fish.

Toy for dolphins

Besides sea cucumbers dolphins are known to play with sea weed, sticks, sponges, shells, coral and even other marine animals like puffer fish. Researchers suggest that it is a fun activity and helps dolphins develop motor skills, solve problems and strengthen social bonds.