Sea cucumbers recycle the seafloor with sausage-shaped bodies
Sea cucumbers are echinoderms of class Holothuroidea—about seventeen hundred eighty-six known species, densest in the Asia–Pacific region. Benthic worldwide, they act as detritivores that break down organic matter so microbes can finish the nutrient loop.
A leathery, elongated body holds a single branched gonad; the cucumber likeness is more than a joke. Like other echinoderms they keep a calcified endoskeleton, usually reduced to microscopic ossicles in connective tissue, sometimes enlarged into armored plates. Shapes run from nearly spherical “sea apples” to serpent-like Apodida or classic sausages; tentacles ring a retractable mouth. Most measure ten to thirty centimetres.
At a glance they barely look like starfish kin: tubular, soft, with bilateral overtones layered on fivefold symmetry still visible as radii from mouth to anus. Humans forage many species as trepang, namako, bêche-de-mer, or balate, and culture some in aquaculture, especially in Asian cuisines.
Their body wall is built of catch collagen that can be slackened or stiffened at will, so an animal can practically pour itself through a narrow gap and then firm up to wedge itself safely inside. There is no true brain, only a nerve ring around the mouth, and a sea cucumber keeps moving even if that ring is surgically removed. Breathing works backwards by our standards: a pair of branching respiratory trees inside the cloaca draws water in through the anus, extracts oxygen and expels it, and the same tubules help flush out ammonia. Extremes span from 3 millimetres to 3 metres long.
An animal that vacuums mud and sells as a delicacy is also an ecosystem engineer. Every swallowed sediment grain is a small recycling plant—proof that odd body plans can do essential planetary chores.
Source: Sea cucumber
