Sea Cucumber (class Holothuroidea)

EchinodermSeabedRecycler

Overview

Sea cucumbers (class Holothuroidea) are soft-bodied, sausage- or worm-shaped animals of the seafloor — and, despite their vegetable-like name and appearance, they are animals, and echinoderms at that, related to starfish and sea urchins. They have a leathery body, a ring of feeding tentacles around the mouth at one end, and rows of tiny tube feet. Hundreds of species live in the ocean, from shallow reefs to the deepest trenches.

Quiet and unassuming, sea cucumbers are vital recyclers of the seabed — and they have some of the strangest defences of any animal.

Note: sea cucumbers are a large and varied class; details here cover them broadly. Treat general statements as approximate and verify against authoritative sources.

Habitat & Range

Sea cucumbers live throughout the world's oceans, on and in the seabed — from coral reefs, seagrass beds, and rocky shores to muddy bottoms and the abyssal depths, where they can be among the most abundant large animals on the deep ocean floor. They are found at all depths, sitting on the bottom, burrowing in sediment, or, in some deep-sea species, even drifting and swimming.

Diet

Most sea cucumbers are deposit or suspension feeders. Deposit feeders swallow sand and mud, digest the tiny organisms and organic matter in it, and pass out cleaned sediment — much as earthworms do on land — while suspension feeders spread sticky tentacles to catch drifting particles and plankton from the water. By processing vast amounts of sediment, they help clean and recycle nutrients on the seafloor.

Behavior

Sea cucumbers are mostly slow-moving, but they are far from defenceless. Many can eject sticky, tangled threads (Cuvierian tubules) from their rear end to entangle a predator, and some take this further by expelling parts of their own internal organs — which can be regrown later — to distract or deter an attacker, a process called evisceration. Some also contain toxins. They breathe partly through internal “respiratory trees,” and a number of small animals, including certain fish, even shelter inside a sea cucumber's body. Many can stiffen or soften their body wall remarkably.

Human Interaction & Conservation

Sea cucumbers are ecologically important seabed cleaners, and they are also harvested in large numbers as a delicacy in some cuisines (often called bêche-de-mer or trepang) — a trade that has overexploited some species and become a conservation concern. They are otherwise harmless to people. Consult authoritative sources for species-specific status.

More photos of the sea cucumber