Sea liliesCrinoidea

Every feather star on this reef spent its childhood on a stalk, cemented to the rock, and then broke off and walked away.

Crinoids are echinoderms, the same phylum as sea stars and urchins, and they are the group that never turned over. A sea star crawls mouth-down; a crinoid holds its mouth upward and its arms open into the current, which is why the whole animal reads as a plant. There is no stalk on the ones you see by day on the reef, just a small cup of a body clinging to a coral head or a gorgonian by a ring of hooked cirri, with ten to two hundred branched arms fanned out above it.

The stalked forms, the sea lilies proper, live deep, below the reef and down the walls, and for a long time they were taken to be fixed in place for life. Then submersible video caught one letting go, hauling itself across the bottom on its arm tips and dragging the stalk behind it like luggage. Slow, ungainly, and unmistakably going somewhere.

Feather stars move better than that. They crawl on their cirri, and when something disturbs them they swim, rowing with the arms in a rolling sequence, half of them beating while the other half recover, so the animal spirals upward before drifting back down to a new perch.

The feeding is done with the fan. Each arm carries rows of pinnules, each pinnule a line of tube feet flicking food particles into a groove that runs down to the mouth, the whole array angled across the current rather than into it. Many species stay balled up in a crevice all day and climb to the highest exposed point at dusk to open. Crinoids are also the oldest surviving echinoderm class by a wide margin, common enough in the fossil record that entire limestone beds are made of their broken stems.