The ocean’s bizarre hydraulic machines are powered by seawater

Nature · Published 29 October 2026 Swipe more like this →

In short: Imagine an animal with no centralized brain that moves using a literal plumbing system. Echinoderms—like sea stars and urchins—don't use blood vessels to circulate nutrients. Instead, they utilize a complex network of water-filled tubes to move, shape their bodies, and navigate the seafloor.

Echinoderms, a phylum meaning "hedgehog skin," represent a masterclass in biological engineering. While humans rely on blood for circulation, these creatures use a water vascular system. Seawater enters through pores—such as the madreporite plate visible on many sea stars or specialized pores in sea lilies—and travels through internal tubes. This hydraulic pressure powers their "tube feet," allowing them to move with surprising agility or maintain their structural shape against ocean currents.

Their anatomy is a study in geometric evolution. While they often display pentameral (five-fold) symmetry, this body plan is actually a developmental twist; larvae begin with bilateral symmetry before reorganizing into the radial forms we see today. Their skeletons are not solid bones but 3-D puzzles of thousands to millions of calcium carbonate components called ossicles, which are infused with tissue and covered by skin.

This diversity spans from tiny sea daisies discovered in the 1980s to massive sea cucumbers reaching two metres in length. Some species, like the sunflower sea star, play critical ecological roles as predators that protect kelp forests. However, these complex organisms face modern threats; for instance, sea star wasting syndrome has caused catastrophic declines, wiping out over 90% of sunflower sea stars in many regions.

The group's history is equally vast, with fossil records dating back to the Cambrian Period (542 to 488 million years ago). From being used as food by ancient Greeks and Romans to becoming objects of superstition in the Middle Ages, echinoderms have remained a constant, albeit strange, fixture of marine life for half a billion years.

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