if you have even been scuba diving or snorkelling
you likely came across turd-like sausages on the ocean floor - Sea cucumbers. Despite their name and their motionless lifestyle,
they are animals. And although they look like a weird sea version
of slugs, worms, or millipedes. they are actually closer related to us humans. Their closest relatives, however, are starfish,
sea urchins and sand dollars with which they form the Echinoderms. Despite Sea cucumbers looking intrinsically
harmless, they are actually quite the opposite if you aren't careful. In this video, we will discuss why that is
as well as everything else that makes these little turds interesting. Enjoy
A defining trait of Echinoderms is their radial symmetry consisting of usually 5 mostly identical
body parts. You can find this symmetry in sea cucumbers
too but it's far less obvious than in sand dollars or starfish for instance. If you were to stand a sea cucumber upright
on its mouth or its anus you can however still see the symmetry in the 5 body segments that
connect these two points - at least in some species. So in comparison to starfish and sea urchin,
sea cucumber essentially lay on their sides. Because of this, they have also evolved a
weak bilateral symmetry as their individual segments have developed differently. 3 of them form the trivium, the food so to
speak. while the 2 other form the bivium, the dorsal
face. Each of the segments has a row of tube feet,
similar to those you can find on the underside of starfish, that allow the animal to crawl
along. On the dorsal face, these tube feed are often
under-developed or are lacking altogether. Other species have repurposed them as a form
of protection or as sensory organs. The ring of feeding tentacles around the mouth
are similarly modified and enlarged tube feet. These can be retracted into the body by a
set of retractor muscles when they feel threatened. Additionally, 5 lengthwise running bands of
muscles allow the sea cucumber to expand and contract its body. See cucumbers don't have a brain. instead, they have a simple system of nerve
strings that extend from a nerve ring near the mouth, the central hub of the sea cucumbers
anatomy. and run longitudinally along the walls. With this rudimentary nervous system, they
are able to detect touch and chemical stimuli and coordinate all their bodily functions
including their movement. responsible for locomotion in sea cucumbers
like in all echinoderms is the water vascular system, a system unique in the animal kingdom,
that works almost entirely hydraulically, so through water pressure. In starfish, part of this system is a sieve-like
orifice on the upper face on the animal through which they can take in seawater. In sea cucumber, however, this sieve is regressed
making their water vascular system a closed circuit. Other than that they work almost entirely
the same. From the central ring canal, 5 rows of canals
branch out to each row of tube feet. Each of these canals is connected to hundreds
of ampullae, little sack-like structures that expand when water from the radial canal is
pumped into them. Each ampulla is linked to a single tube foot. Through contraction of the sac the sea cucumber
force water into the tube foot, causing it to extend and push against the ground. minute muscle controls the direction in which
it points. Similarly, a relaxation of the sac makes the
foot retract again. Through hundreds of these little feet, individually
but coordinately controlled, sea cucumbers are able to crawl along in any direction,
but only very slowly. Similarly, spectacular is their respiratory
system because sea cucumber essentially breath through their butts. their main respiratory organs are two trees
of hollow highly branched tubes, called water lungs. these trees are attached to the cloaca of
all things. By closing their anal sphincter muscle they
can force the water into the system, allowing them to breathe
Even more absurd is that some animals, after analysing their options, decided that this
is the best place to live, inside the cloak of sea cucumbers. A variety of fish, most commonly pearl fish,
as well as a few species of scale worms, and also some crabs use the anal cavity of certain
sea cucumbers for protection from predators. these are so-called commensalistic symbiotic
relationships, so relationships that as opposed to parasitism, or mutualism benefit one side
and down negatively impact the other. Still, some species of the sea cucumbers have
developed anal teeth, presumedly to keep the unwanted house guests out. Sea cucumbers can be found in every ocean
around the world, in shallow waters as well as the deep sea, down to depths of up to 10km.
on the deep seafloor they make up the majority of the animal biomass, up to 95% in some places. Here giant herds of seacucumbers, consisting
of millions of animals wanter across the ocean floor in search of food. In addition to their numbers, they are also
surprisingly diverse. Over 1700 species are known today. The biggest of them (Synapta maculata) can
reach a length of up to 3m, the smallest measure only a few millimeters (Rhabdomolgus ruber). Typically however, they are between 10-30cm
long. Sea cucumbers feed on detritus and debris,
algae and plankton. Essentially everything that ends up in their
mouths and is useable gets processed. They typically use one of two strategies to
acquire their food. Some species are filter-feeders. These usually have developed large feathery
tentacles that they flail in the water column to catch free-floating plankton
But most of them are sediment feeder that use their tentacles more like shovels to fill
up on mud on sand from the ocean floor. These materials then make their way through
their intestines while the organic matter in it is digested. During this process, the organic particles
are broken down into far tinier pieces, which are then excreted together with the undigestable
sand and will become fodder for even smaller lifeforms. So similarly to earthworms in terrestrial
ecosystems sea cucumbers by filtering sediments and recycling nutrients back into the food
web, play a major role in the biological processing of the seabed. A single specimen can digest more than 45
kg of sediment a year. Legend has it that every grain of sand in
the ocean has at some point or another been excreted by a sea cucumber. Even their reproduction seems perfectly fitting
for their crude lifestyle. Instead of going through the trouble of dating,
they simply release both eggs and sperm into the surrounding water hoping that they meet. to maximize fertilization success this usually
happens simultaneously in an area. Sea cucumbers are also notable because they
possess diverse regeneration abilities. Some species have the ability to recover from
the loss of 50% or more of their body which they sometimes use deliberately to reproduce
asexually. basically, the sea cucumber splits itself
in half and each half regrows into a full sea cucumber. Other echinoderms such as Starfish have similarly
the ability to regrow lost body parts. Some can regrow limbs and a few can even regrow
a completely new body from a single arm even from an arm fragment just 1cm long. As cool as this is, it doesn't change the
fact that on the face of it sea cucumbers are quite benign animals and seemingly easy
prey for predators. However, the majority of them have, despite
their apparent helplessness, developed effective defence mechanisms. many of them use the most obvious method of
protection for such an animal, toxin. Most species carry a toxin called Holothurin
in their organs some can even release it through their skin when they feel threatened. This toxin is so effective in killing small
animals particularly fish that it was even used by fishermen from indo-pacific regions
to hunt fish. most sea cucumbers have in addition to that
the absurd ability to expel their inner organs from their butts sometimes from their mouths
and discharge them into the surrounding water. This is called evisceration and is meant to
distract or scare predators away. As brutal as this seems this behaviour does
not kill the sea cucumber. As mentioned earlier they have incredible
self-healing capabilities, which allow them to simply regenerates the organs in the following
weeks. A few species have even developed a special
organ for that purpose, so-called Cuvierian tubules. These are long white tubes that are attached
to one, or both, respiratory trees. If the cucumber is attacked by a predator
it will expel these sticky, stringy sometimes toxic threads out of its anus. The resulting net of strings can entangle
immobilize and even kill potential predators and gives the sea cucumber the opportunity
to crawl away. this is yet another way these sedentary animals
can defend themselves. As a result of these multifaceted defence
mechanisms, sea cucumbers are typically avoided by generalist predators. A few highly specialised ones, however, do
prey on them. Among them two species of sea snails. The giant tun and the partridge tun. These basketball sized snails are immune to
the sea cucumbers toxin, they have, however, their own very potent poison that they use
to paralyze the sea cucumber. POKEMON FIGHT
Because I guess when you are a snail, a sea cucumber running away from you is a real concern. Paralysed and with their toxins not affecting
the snail the sea cucumber then has to has to experience being swallowed whole and alive. Which concludes the most boring hunt in the
animal kingdom. For humans touching sea cucumbers is Aside
from allergic reactions to their toxin generally not life-threatening. The contact with their toxic threads, outer
skin, or ejected innards can, however, cause sometimes painfull skin irritations maybe
similar to jellyfish stings. If the toxins come into contact with your
eyes they can even cause blindness when left untreated. So as long as you don't know what you're doing
and what kind of sea cucumber you have in front of you You're probably best advised
to leave them be. needlessly stressing wild animals by touching
and picking them up, is a douchy thing to do anyway. just watch them from afar. That being said, not every sea cucumber species
is poisonous. The ones that aren't and even a few that are,
are often considered a delicacy in many places, particularly in Asia in countries such as
China and Japan. In Japan, the history of sea cucumber fishery
dates back over 1000 years to the 8th Century. Here sea cucumbers are traditionally served
in the form of a soup. But this too isn't always safe. I can happen that species get confused or
meals aren't prepared correctly. When that happens and you accidentally eat
a poisonous sea cucumber the effects are a lot worse. It can cause severe abdominal pains and vomiting,
numbness and breathing difficulties. A few people have even died after eating poisonous
sea cucumber But given how many tons of sea cucumber are
eaten every year these cases are extremely rare. Because of an ever-increasing demand over
the past few decades particularly in China substantial numbers of sea cucumbers are now
bred and cultured artificially in seawater ponds or sea ranches. depending on the regions is takes between
2-6 years for an individual to grow to a marketable size. The Japanese sea cucumber is the most important
and valuable commercial sea cucumber species and China is by far its biggest producer. Their Total production amounted to 200 000
tonnes in 2017. This makes sea cucumber farming a multi-billion
dollar industry for China(4.44 billion). But not every sea cucumber was content with
their lives as the vacuum cleaners of the oceans. Some of them have developed bodily features
that allowed them to lift themselves up from the ocean floor and take to the skies. 26 of these swimming sea cucumbers are currently
known but it is suspected that there are more of them. Most of these inhabit the deep sea and are
incredibly rare, which is why it is understandably difficult for scientists to shed a light on
this remarkable and elusive subset of sea cucumbers
The most famous of them is probably the fittingly dubbed headless chicken monster. Theses equally beautiful and bizarre looking
sea cucumbers have repurposed some of their tube feet and developed them into three webbed
veil-like sails. Like their ground-bound relatives, these sea
cucumbers are sediment feeder. in between meals, however, they spend most of their time
swimming, using their sails to sometimes rise as much as 1km above the ocean floor. This allows them to avoid ground-living predators
and to find better feeding grounds. Pelagothuria natatrix another species of swimming
sea cucumber takes this way of life to the extreme. They have left their groundliving lifestyle
behind completely. Unlike the previous example they spend their
entire life off the sea floor using their feeding tenticles ontop of their almost circular
umbrella to catch plakton and algae. They are the only known sea cucumber even
the only known echinoderm that conquered the open ocean .
All this makes sea cucumbers truely amazing little animals that even after more than 350
millions years on this planet are still going strong and as succefull as ever.
tl;dr: They aren't
It's highly unlikely something as complicated as anal teeth evolved to keep those creatures out if there was no disadvantage to having them in there. I only know what's in this video, but I therefore question whether those sneaky creatures are commensalistic.