Squishy Echinoderms of Singapore

Strange as it may seem, these squishy animals are the cousins of sea stars.

Here's more about the sea cucumbers of Singapore!

Sea cucumbers are animals!! They are NOT vegetables as their common name suggests.

Like sea stars and other echinoderms, sea cucumber have five part symmetry. They are symmetrical along the body length, with five rows of tube feet along the body.

The psychedelic Sea apple sea cucumber (Pseudocolochirus violaceaus) has five rows of bright yellow tube feet along its round apple-like body. This sea cucumber is only sometimes seen on our remote shores and is listed among the threatened animals of Singapore. The longer bright orange sea cucumber is sometimes common. We have yet to find out its identity.

These smaller colourful sea cucumbers are sometimes commonly seen on our Northern shores, among seagrasses. The Warty sea cucumber (Cercodemas anceps) in the left photo, has bumps on its body. While the Thorny sea cucumber (Colochirus quadrangularis) in the right photo, has soft pointed projections in five rows along the body length.
Instead of lying on their mouths like sea stars, sea cucumbers lie on their sides. The mouth is on one end and the backside on the other. At the mouth are modified tentacles that look like a flower. These tentacles gather edible bits from the water or surface.

Other sea cucumbers are well camouflaged. The Blotchy sea cucumber (Actinopyga lecanora) is a large smooth sea cucumber that is commonly seen among coral rubble and reefs on our Southern shores. It comes in a wide range of subtle colours and patterns that blend in with the surroundings. The animals in the photos above are both Blotchy sea cucumbers. This sea cucumber is identified by the white or greyish zone around the backside end. The anus is guarded by five teeth-like structures!

Why would a sea cucumber have teeth on its butt?

A good question! While we don't know for sure why some have teeth, we do know that some creatures actually live inside a sea cucumber's backside?

Why would anything live in a sea cucumber's butt?!!

A unique feature of some sea cucumbers is an internal breathing system of branching tubes along the length of their bodies. Called respiratory trees, most large sea cucumbers have a pair of these, each connected to the opening on the backside. To breathe, the sea cucumber pumps water in through its backside and up through the respiratory trees. The water is then flushed out through the backside again. With this constant flow of water, some tiny creatures may find the backside of a seacucumber a cosy but well ventilated place to be! These include pea crabs and the Pearlfish.

Some sea cucumbers are well hidden. These two sea cucumbers can be commonly seen on undisturbed sand bars and near seagrass areas on our Northern shores. They are both listed among the threatened animals of Singapore.
The Sandfish sea cucumber (Holothuria scabra) in the left photo, has a long body with a distinct upper and underside. The upperside is rounded, darker and often has little folds with faint black bars; in fact, we usually call it the 'Garlic bread' sea cucumber because that's what it looks like! The underside is paler and usually flat. The Ball sea cucumber (Phyllophorus sp.) in the right photo, is usually well hidden in the sand. A sand bar may be home to hundreds of these sea cucumbers.

On our Southern shores, these Long black sea cucumbers (Holothuria leucospilota) are commonly seen.
They are usually well hidden under rocks or coral rubble. Only a small part of their body is extended out of the hiding place, to gather edible bits from the sand with their feeding tentacles.

Some sea cucumbers are mistaken for worms!

Synaptid sea cucumbers (Family Synaptidae) are often found draped around sponges, sometimes in large numbers. These sea cucumbers have thin body walls.

Being soft and slow, sea cucumbers protect themselves by hiding or being unpleasant to deal with. Some have toxins or distasteful substances in their bodies.

To repel and distract predators, some sea cucumbers vomit their entire digestive system and other internal organs such as the respiratory tree and even their reproductive organs. Depending on the species, these can emerge from the front or back end of a sea cucumber. Some species eject toxic or sticky strings (called Cuvierian tubules) from their backsides. These immobilise the predator in a gummy mess or release toxins. The sea cucumber eventually regrows its innards and arsenal of Cuvierian tubules.

There are many other kinds of sea cucumbers seen on our shores besides those featured in this article. Some are tiny, others are well hidden.

More FAQs about sea cucumbers

Since sea cucumbers can regrow their innards, can I poke one to make it vomit? Please don't make sea cucumbers expel their intestines. Not all do this. Those that do cannot eat until they re-grow their innards.

Can I eat the sea cucumbers I see on the shore? Some large sea cucumbers are considered delicacies and harvested for food. The harmless Sandfish sea cucumber (Holothuria scabra) is among those species of sea cucumbers that are collected as a Chinese delicacy. They are gutted and dried for sale as ‘trepang’ or ‘beche-de-mer’. Tests indicate these sea cucumbers contain toxins. They must be properly prepared before they are safe to eat.

Should I collect sea cucumbers for my home aquarium? Some colourful sea cucumbers are harvested for the aquarium trade. Ironically, they do not make good aquarium specimens as they are often toxic to their tank mates. The Sea apple sea cucumber, for example, has been described as a 'bomb' that can wipe out the entire tank.

Why is collection of sea cucumbers a problem today? Collection of the some sea cucumbers has been a traditional activity for centuries in many coastal peoples in many parts of the world ranging from Madagascar to the Philippines. However, the recent high market price of this delicacy has resulted in increased collection in recent decades. Some edible sea cucumbers are globally threatened by over-collection. In some areas, such sea cucumbers have become scarce. In others, specimens collected are smaller and have to be harvested from deeper waters. Efforts to culture these edible sea cucumbers have only just started.

More links to sea cucumbers
Lane, David J.W. and Didier Vandenspiegel. 2003. A Guide to Sea Stars and Other Echinoderms of Singapore. Singapore Science Centre. 187pp.