Today on Blue World Academy, Sea cucumbers!
Virtually everyone is familiar with the sea star, an animal which is a member of the phylum
of invertebrates known as Echinoderms, meaning “spiny skin.”
Other Echinoderms include the sea urchins and the feather stars.
The sea cucumber is another echinoderm—hard to believe since most of them don’t have
very spiny skin at all.
But the sea cucumbers are most closely related to sea urchins!
There are over 1700 species of sea cucumbers in the world’s oceans, and it’s not hard
to guess how they got their name.
Most are about the size and shape of a large cucumber.
But the similarity to a vegetable ends there!
Sea cucumbers have tiny tube feet like sea stars and sea urchins.
They can move around, albeit somewhat slowly.
There are two basic ways in which sea cucumbers feed.
The plankton-feeders extend feathery tentacles into the water as a net for passing plankton.
The sticky tentacles gather up particles, then one by one, the sea cucumber licks the
plankton off each tentacle with a centrally-located mouth.
In the rich waters of New England, an Orange-footed sea cucumber feeds on plankton soup.
If I tickle its tentacles, the sea cucumber withdraws them for protection.
Other species of sea cucumbers feed by digging though the sediments on the sea floor looking
for decaying particles.
They typically eat a bunch of sand in the process, which passes completely through their
digestive tract.
It’s a slow process, but seen in a time lapse, a Tiger tail sea cucumber covers a
lot of ground looking for food.
You might think that an animal like this would be defenseless, but in fact many sea cucumbers
possess a fascinating defense mechanism.
When threatened, they can eject a sticky goop called cuvierian tubules to ensnare predators.
Others can expel poisonous chemicals to drive predators away.
As a result, very few animals will dare to attack sea cucumbers.
Due to that general lack of predators, sea cucumbers make a safe home for symbiotic partners.
An Emperor shrimp lives in safety on a sea cucumber and in exchange for the protection,
keeps its host free of parasites.
But of course, there are a few predators that can handle the sea cucumber’s defenses.
In the north Pacific, Giant Sun stars will attack and eat sea cucumbers.
And in the south pacific, a large snail known as a Partridge Tun specializes in eating sea
cucumbers using a powerful venom to subdue its victim.
The Echinoderms are a diverse and interesting group of animals, with the sea cucumber as
its strangest and possibly most fascinating member.