Sea Cucumber

Image via Wikimedia

In case you hadn't noticed, echinoderms are really weird. They're so weird that when one has a head and a tail, it's a unique and interesting characteristic. Sea Cucumbers are those wacky echinoderms, selling out to the Bilaterians and acquiring a head, a tail, a left and a right.

Other echinoderms stick to their Radiata roots. They have a top and bottom, but everything radiates like the arms of a starfish or the spines of a sea urchin. Sea Cucumbers can be thought of as a sea urchin on its side. Food once went up from below and out through the top, now it goes in on the left and out through the right.

Indeed, some Sea Cucumbers are virtually spherical, others are long and look like a worm. The smallest are just 3 millimetres (0.12 in) long, the largest are more like 1 metre (3.3 ft), most are 30 cm (1 ft) at most.

Image via Wikimedia

They lead very humble and, from our perspective, rather disagreeable lives. Not for them the spectacular, the graceful or the underwater soaring and surfing. Their lives are instead concerned mostly with mud. It could be the mud around and beneath the vibrant colours of shallow water coral reefs, it could be the grim deserts of mud at the bottom of the deepest seas. But it's mud. And not the anti-ageing, cleansing, rejuvenating, exfoliating mud, either. Just mud.

It's for this reason that they are so important for the marine ecosystem. You can give them a boost in self confidence and say they are part of "The Clean Up Crew." That'll put a smile on their excuse for a face!

Being an echinoderm they have those tube feet, hundreds of them, in 5 rows. Since they are on their side, the 3 rows of tube feet that are always in contact with ground are well developed, whereas the others on what you would call their back are not so good and sometimes absent entirely.

Image via Wikimedia

At the mouth, between 8 and 30 tube feet have become tentacles for shovelling food in. This will be tiny bits of algae, plankton or dead and dying organic matter. The tentacles can be used to capture these morsels right out of the water, others just guzzle mouthfuls of mud and digest whatever happens to be digestible. This is why they are so successful in the deep: they can just swallow the ground they're walking on and eat any crumb of actual food, even if it's a crumb that sank miles from the surface.

And yet, despite everything, or perhaps despite anything I have to say, Sea Cucumbers still guard their lives jealously. It just seems that they can't help but be utterly disgusting in doing so.

Image via Wikimedia

One thing they can try out is hiding in a little crevice somewhere. It helps that they have almost no skeleton to speak of. Whereas other echinoderms have large plates of calcium carbonate, most Sea Cucumbers have only very tiny ossicles under their skin. Their utterly extraordinary skin. Skin made of a collagen that can, AT WILL, be made either stiff or soft. It means they can turn themselves into a not-quite-ready jelly,  pour themselves through a crack and then go back to normal again. Amazing!

And it makes me wonder if all that mud actually is anti-ageing, cleansing, rejuvenating and exfoliating after all.

Another thing they can do is called... EVISCERATION.

It's about as violent as it usually is, it's just that the Sea Cucumber can recover from it rather than just quickly die.

Basically, it shoots out a bunch of internal organs through its rear end. This stuff is sticky and toxic to many fish and crabs. Surely a bit traumatising, too? I mean, a load of internal organs fired into your face? People these days like their meat to be amorphous polygons of flesh, not organs and carcasses with lifeless eyes. Imagine if abattoirs worked by scaring cattle into firing out a few internal organs while the actual cow ran off! The Sea Cucumber regenerates its lost innards in a few weeks, so it would even be a renewable resource!

I'm afraid we shall have to take a closer look at that rear end. A good, long, inquisitive stare.

Image via Wikimedia

It's a "cloaca", which means it's a multi-purpose opening. Most vertebrates have one for excretion, egestion and reproduction - we mammals are actually quite odd for the division of labour we employ. But Sea Cucumbers also breathe through it! When we humans pass air through the posterior aperture people laugh, frown or say "whoever smelt it, dealt it". For Sea Cucumbers it'a just normal breathing. I'll take our way, for fun if nothing else.

Some creatures seem to find this cloaca very intriguing indeed. Crabs and worms might live in it. There are even fish who use it as a place to stay when they are young, protected from predators and picking out bits of food from the passing... processed mud. Ahem. I'm starting to think that this mud must be utterly wonderful stuff, perhaps properly magic! What a life... I hope it's worth it!

Mating doesn't involve the cloaca at all, thankfully. Most Sea Cucumbers release sperm and eggs into the sea through a hole near the mouth tentacles. Most will develop into tiny larvae in a few days. These are free swimming, using cilia to get around. They have so much to look forward to.

Some Sea Cucumbers fertilise their eggs internally and put them in a pouch, almost like a marsupial. Others develop their young within the body and give birth later. The cloaca isn't involved in this process, which is good. If they gave birth through their anus, the fish and crabs living there might eat their young. I can't believe I have found cause to write that sentence.