The class Holothuroidea contains sea cucumbers. There are approximately 1,150 species of sea cucumbers. Like most echinoderms, sea cucumbers are found in most oceans and at depths that range from the shallows to the deep sea. They are very numerous in the sandy areas of coral reef lagoons. Here they are often referred to as the “vacuum cleaners of the sea” because of their feeding habit of mopping up debris that falls from the water above. Sea cucumbers are also interesting in that they were Australia’s first export item. Indigenous Australians from north west Australia used to export sea cucumbers to Chinese traders as early as the 16th century. This was at least 200 years before the European invasion of Australia.

• To be a fleshy, sausage-shaped echinoderms
• To have most of your internal skeleton reduced so that the outer part of your body is essentially a tough leathery skin
• To have tube-feet with suckers on the end of them.
• To be able to defend you self by throwing up your entire digestive system (Good trick eh!).
• To be a deposit feeders which specialised tube-feet around your mouth to help mop up potential food containing particles.5. To be a deposit feeders

Sea cucumber, bech l’mar.

Sea cucumbers are shaped like a big sausage. They have a distinct upper (“dorsal”) and lower (“ventral”) surface with tubefeet only being found on the upper or surface. Although sea cucumbers have reduced body armor in the form of a calcified shell, they often have protuberances that function to look like armor. Other species are carefully camouflaged so as to look like rocks and other surfaces underwater. The front end of sea cucumbers consist of a set of tentacles that are used to mop up food particles. Some have tentacles that they put up into the water column to filter the water overhead. Not all sea cucumbers live above the sand. There are some which spend their lives burrowing through the sediments of coral reefs and other areas of the world. These are just like giant earth worms and ingest the sediments as they burrow. The sediments that are ingested are sorted and the edible particles absorbed. The rest of the sedimenst (grit and rubble) are expelled out the back end of the sea cucumber.

Sea cucumbers live in all oceans and spend their time either lying directly on the sediments or burrowing through the sediments. Sea cucumbers can be easily found on coral reefs for example, lying in the shallow water at low tide. Generally, they are immobile until the sun sets. At this time, sea cucumbers become very active and begin to feed. Sea cucumbers move principally using their tube feet and rhythmic contractions of their large fleshy bodies. Burrowing sea cucmbers move through the sediments using rhythmic contractions of their body musculature. Some deep sea forms actually use the rhythmic contractions of their bodies and large fleshy protuberances to swim. One example, Scotoplanes globosa, can be collected from 3400m or 3.4 km deep in the sea! .

Sea cucumbers are almost all detritivores. This means that they eat the tiny scrap particles that are usually abundant in the environments that they inhabit. There are two basic modes of feeding among sea cucumbers. “Direct deposit feeding” is one method which is seen in many surface dwelling and burrowing species. In this feeding method, sea cucumbers literally wipe their tentacles over the sediments to pick up tiny particles that settle there from the water above. Sea cucumbers are efficient direct deposit feeders. The fact that fecal pellets (poo) are richer in terms of energy and nutrients than the surrounding sediments that sea cucumbers eat is testimony to this fact. The other mode of feeding is the suspension feeding. Suspension feeding sea cucumbers have finely diverticulating buccal tentacles that are used to pick particles out of the water column during feeding.

Sea cucumbers have tough skins that probably lessen the risk of predation. However, they do face the problem of being eaten by large fish. Sea cucumbers, however, don’t just lie around and let this happen. They have a number of neat tricks. The first is that some sea cucumbers have the ability to throw up their entire digestive systems! They do this to distract the predator who generally focuses on the yummy bits thrown up with the stomach. The sea cucmber then crawls away and regrows its entire digestive tract over the next couple of months. Amazing huh! The second trick is that some other sea cucumbers have fine sticky threads that they are able to eject out their bottoms when trouble brews. These threads are called Cuverian Tubules and are as sticky as any glue you can buy in a shop. These threads are thrown out over the potential predator who gets them stuck all over it. This usually makes the potential predator desist from attacking the sea cucumber.

Sea cucumbers tend to be have separate sexes. Spawning behaviour tends to be seasonal. Many sea cucumbers on the Great Barrier Reef spawn during the mass spawning events seen in November. During spawning, sea cucumbers travel to the top of reef structures and release their gametes into the surrounding currents. A range of developmental modes is seen among sea cucumbers. Development via feeding larvae (Planktotrophy) or non-feeding larvae (lecithotrophy) occur in a large number of species. In others, embryos and larvae may be brooded by the female. The feeding larva of sea cucumbers (when present) is very distinctive and is called an auricularia larva. Itswims for about 10-40 days before settling on the bottom and metamorphosing into a baby sea cucumber.

There are a number of animals that live with sea cucumbers. Tiny polychaete worms that look almost identical to the skin of the sea cucumbers crawl across the skin and are probably responsible for cleaning the surface of the sea cucumber in return for getting a place to live. There are also some very strange relationships. There is a little fish that lives in the back end of sea cucumbers. Again, in return for being a cleaner, the fish gets a pace to live and something to eat!

Sea cucumbers are harmless. Unfortunately, they are good to eat and are considered a delicacy by many cultures. Did you know that a ton of dried sea cucumbers will fetch as much as a million dollars in some countries? This has lead to uncontrolled exploitation of sea cucumbers around the world. In some places they have almost completely disappeared. Several projects (e.g. Solomon Island) are currently underway to start growing sea cucumbers in aquaculture farms to try and reduce the fishing pressure on sea cucumbers. Sea cucumbers are seriously endangered in many parts of the world.