May 16

This is the most enduring friendship on Earth: 250 million years still together and never leaving

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Sea lilies and anemones have been friends for millions of years, and this relationship is still going smoothly.

Off the southwestern coast of Japan, a group of animals coexisted in a close relationship that researchers say has disappeared in modern times.

A team of researchers from Japan and Poland has found a sea lily – it’s an animal, not a plant – that hosts corals and anemones on its body, in a relationship surprising symbiosis. These creatures were last seen “roaming” together in fossils that are older than the time of the first T.rex dinosaur. So finding out that their friendship was still alive and well was an unexpected turn of events.

The Japanese sea lily is about 60 cm tall and belongs to the class crinoid, an animal related to sea urchins and starfish. Corals are known as the home of sea lilies and they also share their space Metridioidea, a species of sea anemone.

Sea anemone resides on the body of a sea lily.

In a new paper published in the journal Palaeogeography, the team describes how corals and sea anemones attach to sea lilies, a common species collaboration in the Paleozoic deep sea, in an era that has ended a quarter of a billion years ago. But this cooperation disappeared by the end of the Paleozoic, when the fossil record of these animals co-existing did not exist.

According to Mikołaj Zapalski, a paleontologist at the University of Warsaw and lead author of the study, the most recent fossils of crinoids and corals coexisting in this fashion are 273 million years old. Zapalski says that corals and crinoids are also found in fossil deposits younger than the Paleozoic (ending about 250 million years ago), “but for unknown reasons they were never found with together”.

So the team was quite surprised when they discovered these animals were actively socializing in the deep waters off the coast of Japan.

Entire body of sea lily, with arrow indicating location of polyp Metridioidea.

Although there is sometimes competition for food, the relationship has its own benefits, the researchers say, because corals can, thanks to sea lilies, rise higher from the seabed to make contact. with stronger currents to feed. And small boneless creatures like sea anemones can rely on the branched structure of sea lilies to hold on in the face of drifts.

The team used nets to collect samples in Shikoku’s Sukumo Bay in 2015, detecting the presence of Metridioidea polyps on sea lily stems. Excited by this finding, they searched and dredged other specimens at the bottom of Honshū’s Suruga Bay in 2019. They analyzed these specimens under a stereomicroscope and the stalks of sea-lily appeared, like sturdy steel stakes for coral to cling to.

Not as flashy and dramatic as the discovery of a new shark or a deep-sea glowing fish, but the discovery of this ancient relationship that still exists today is a reminder. Reminds us how little we still know about what’s going on at the bottom of the ocean.


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Entire, sea lily


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