What is a sea cucumber?
Sea cucumbers are bizarre little creatures with soft leathery skin and tentacles protruding from around their mouths. These tentacles can be finger-like, feathery or flattened.
Known scientifically as holothurians, sea urchins are part of the echinoderm family which includes the symmetrical seas stars, sand dollars and sea urchins. Echinoderms have calcified skeletons just below the skin.
Sea cucumbers are the earthworms of the sea floor. They feed on small pieces of debris, tiny sea creatures and algae, breaking them into smaller particles that bacteria can further break down.
There are over 1400 different known species of sea cucumbers which range in size from 1 cm to a whopping 5 meters long .
Sea cucumbers are a prehistoric creature, with fossils that have found that date back over 400 million years. This is about the same time animals with backbones first emerged from the oceans.
Where do sea cucumbers live?
Sea cucumbers live on or under the ocean floor at all depths, from shallow tidal waters to the vast underwater canyons in the deepest oceans.
Some sea cucumbers have tiny "feet" which they use to move along the ocean floor, though most use muscular contractions to "worm" there way around.
Some holothurians inhabit areas with coral and sea grasses, while others live in areas which are nothing more than huge underwater mudflats. Many sea cucumbers bury themselves in the sand or mud, leaving nothing but their tentacles sticking out.
How do sea cucumbers reproduce?
Unlike earthworms which are hemaphrodites, the vast majority of sea cucumbers are either male or female, though a few species can change from female to male when the need arises. The male and female cukes approach each other in the water, court, then eject their sperm or eggs together into a big cloud.
A few species of sea cucumbers are known to carry their fertilized eggs inside their bodies. The mother will pick up the fertilized eggs with her tentacles and deposit them into a pouch on her body.
A few other species will mate with the male depositing his sperm inside the female. The female will carry the fertilized eggs in her body until, after a period of of incubation, she will eject the hatched babies through an opening near the her anus.
How do sea cucumbers defend themselves?
Some sea cucumbers have an especially gruesome response to stress - they will violently contract their abdominal muscles and disembowel themselves by expelling their guts from their anus!
Other sea cukes have specialized sticky filaments surrounded by a viscous poison inside their bodies. They will eject these filaments towards an approaching predator and if the predator becomes entangled in these sticky strings it will die.
Ejecting either their internal organs or the filaments does not kill or hurt the sea cucumber. The organs or filaments eventually grow back..
Sea cucumber feeding itself.
How do sea cucumbers eat?
Each of these echinoderms has between 8 and thirty tentacles which it uses to gather food. Some sea cukes are passive feeders and position themselves in sea currents so they can gather up food which floats by. Others actively seek food, sifting through mud for delectable morsels to eat.
When the food is caught up in its tentacle, the sea cucumber will shove its entire tentacle in its mouth.
What is a sea apple?
A sea apple is a sea cucumber of the Paracucumaria or Pseudocolochirus species. It is the "pretty one" of the sea cuke family, and is found mainly in the Indio-Pacific waters.
The sea apple is more round and more colorful then its sea cucumber brethren, but it eats and moves much the same way. Some sea apples will swell themselves with water in order to float to a new location.
Can I keep a sea cucumber or sea apple in a marine aquarium?
It is not recommended to keep one of these unusual echinoderms in the home aquarium unless you are an experienced aquarist and have a reef-type tank with live rock. Even experienced salt-water aficionados have had difficulty keeping a sea apple or sea cucumber alive.
A home aquarium will not usually produce enough of the minuscule algae or food the creatures need to survive, and they may end up shriveling away to nothing. There are food supplements available if needed, although some sea cucumbers will not adapt to it.
Certain tank mates like crabs like to pick at the sea cukes tentacles, which may cause the cucumber to release its filaments into the water, poisoning the entire tank. You will have to ask yourself if it is worth the risk to your investment.
Do people eat sea cucumbers?
Many Asian countries consider the meat of a sea cucumber as a delicacy. It is used in stews, soups and in sushi. The meat is bland, but readily absorbs the flavors of the food it is cooked with.
Sea cucumbers can be bought and prepared fresh or can be found in specialty stores as a dried product.
Cukes are also said to have many health benefits because it is rich in niacin, calcium and lysine.
- Chimaera and Other Strange Ocean Creatures
A illustrated look at some strange and scary ocean dwelling fish and other critters.
Kristen Howe from Northeast Ohio on April 03, 2016:
Gable, you're very welcome. Oddball life is all right with me.
Gable Rhoads (author) from North Dakota on April 02, 2016:
Hi Kristen. I love the oddball life on earth! Thanks for stopping by.
Kristen Howe from Northeast Ohio on April 02, 2016:
Gable, I've heard of sea cucumbers and not of sea apples. Lovely photos with interesting facts about these amazing marine creatures. Thanks for sharing.
Mary Norton from Ontario, Canada on November 12, 2014:
I have seen many sea cucumbers and I have seen people along the sea coast in the Philippines dry these. These can be sliced and added to some Oriental dishes. Lovely pictures.
Gable Rhoads (author) from North Dakota on May 30, 2013:
Hi pinto2011, thank you for stopping by and commenting. :)
Subhas from New Delhi, India on May 29, 2013:
Hi Gcrhoads64! This is indeed a very interesting well described article on something which was completely unknown Hi to me.
Gable Rhoads (author) from North Dakota on May 29, 2013:
Thank you, prasetio30. They are pretty cool creatures. :)
prasetio30 from malang-indonesia on May 29, 2013:
I had never seen something like this before. I learn many things here about sea cucumber. Nice pictures selection as well. Thanks for sharing with us. Voted up!
Gable Rhoads (author) from North Dakota on May 29, 2013:
Thanks, for the support, livingsta. Yes, they are interesting and oddly beautiful. :)
livingsta from United Kingdom on May 29, 2013:
Thank you for this interesting hub. They are in fact interesting creatures aren't they? Enjoyed reading the hub and the photos are lovely!
Voted up, interesting and sharing!
Gable Rhoads (author) from North Dakota on May 23, 2013:
Hi kidscrafts. They are pretty fascinating and not well-known creatures, so naturally I am drawn to them, too. ;)
Thanks for reading and commenting. :)
kidscrafts from Ottawa, Canada on May 23, 2013:
Very interesting hub about sea cucumbers! I didn't know there were so many species and for sure I didn't know their defense techniques!
Thank you for sharing all those interesting facts, Gcrhoads64!