Sea cucumbers made news not long ago for a new conservation effort in Sri Lanka. It seems they’ve been over-harvested in many tropical regions across the world. This came as a surprise to me – I saw quite a few while snorkeling in Hawaii. It turns out some sea cucumbers are being depleted – it’s not so much that they taste good; they’re said to be so bland they’re often boiled in meat broth to add flavor. But they contain some unusual nutrients, and their resemblance to a certain human anatomical part has given them an unfounded reputation for increasing virility.
Let’s hope sustainable practices prevail, because there’s plenty to admire about living sea cucumbers. Belonging to the class Holothuroidea, they stand out among the other classes in the phylum Echinodermata. Starfish are a good example of a “typical” echinoderm – radially symmetrical, with five arms (pentameral symmetry). Echinoderms are, in general, pretty slow-moving. Most travel on tiny feet – tube feet — which are operated hydraulically, using the water vascular system that is another unique feature of this phylum.
Unlike other echinoderms, sea cucumbers have adopted a worm-shaped (or really, sausage-shaped) body plan. But the five divisions of the body are still evident, separated by grooves, ridges, or rows of tube feet, running lengthwise along the body. Their elongated, five-part shape can indeed bear a remarkable resemblance to a cucumber, although the color varies widely.
Sea cucumbers bear five sticky tentacles, which they use to collect organic matter, either from the sand or drifting down through the water. These they insert alternately into the mouth, to pull off food particles. Because the mouth is often occupied, the other end of the digestive tube has become their main respiratory organ. The sea cucumber’s anus, opening and closing as it breathes throughout the day, has proved too inviting for the pearlfish to resist. This long, narrow fish, with a pointed tail, has evolved just the right body shape to easily retreat into the sea cucumber for safety.
But perhaps the strangest thing about the sea cucumber is its ability to expel many of its internal organs when harassed. The benefits are debated, but it likely serves as a distraction in many cases – similar to a lizard’s tail tip that breaks off when attacked. Afterward, the sea cucumber slowly regenerates its discarded organs. There’s plenty of diversity in when, why, and from which end, evisceration occurs. Sad to say, none of this deters the sea cucumber fisherman. But we can all do our part to prevent these vulnerable creatures from being driven to extinction — I’ll have my cucumbers from the garden, please.