‘Fragile’ creatures — covered in bristles — found as new ocean species. See them (2025)

When a tree falls into a river, flows downstream and hits the ocean, its journey doesn’t end there.

The ocean floor is dotted with wood fall, or chunks of wood that make it all the way to the bottom of the sea. The wood provides a welcome source of nutrients and shelter on the barren deep-sea landscape.

Now, researchers studying these small ecosystems collected a piece of wood from the seafloor in the East China Sea — and discovered two new species that called it home.

A trawler was used to pull the wood from a depth of about 1800 feet off the southern coast of Japan, according to a study published April 10 in the peer-reviewed journal Zoosystematics and Evolution.

The wood, just 14 inches long, was stored in a freezer aboard the boat before being transferred to a laboratory and sawed open, researchers said.

When the wood was opened, researchers found 30 saltwater mussels living inside, according to the study. Many of them belonged to known species, but a few had unique characteristics.

Two of the mussels belong to the newly described species Idas sinensis, or the Chinese Idas, according to the study.

The shells of the mussel are “highly elongated” with an “elliptical shape” between 0.36 and 0.52 inches long, researchers said.

The shells are “thin, fragile, deep olive-yellow (and) semi-transparent,” according to the study. The shells also have “very short, dark brown bristles” on the back of the umbo, or highest peak of the curved surface.

Most of the body of the mussel animal was poorly preserved, researchers said, but the foot, or muscular section that extends out of the body to help the mussel move, was purple.

More than 20 of the other mussels found in the wood belonged to a different new species, Idas pacificus, or the Pacific Idas, according to the study.

The Pacific Idas has a more “oval”-shaped shell, though it is still “thin, olive-yellow (and) semitransparent,” according to the study.

The umbo has bristles that are the same color as the shell, with a triangular shape, researchers said.

The foot of this species was preserved, and accounted for about 40% of the mussels total shell length, which ranges from 0.12 to 0.42 inches long.

“Sunken wood provides shelter for a variety of marine organisms, offering both a carbon source and substrate,” researchers said. “... Both Idas pacificus sp. nov. and Idas sinensis sp. nov. have thin and fragile shells, which would offer little protection against predators in more exposed environments. However, the sunken wood provides a natural shielding habitat.”

The shells were both found within holes in the wood, and researchers believe their bristled-covered exterior might help make this possible.

“(Previous research) suggested that the bristles of Idas species may help keep the valves away from the burrow walls and possibly improve water flow around the animals. This hypothesis may partially explain the differences in bristle development between the two species,” according to the study. “Idas pacificus sp. nov., with its shorter and more triangular body shape, exhibits more developed bristles, which may enhance stability in cylindrical burrows.”

The new species were found in the East China Sea, a body of water off the eastern coast of China, south of Japan and South Korea.

The research team includes Qiong Wu, Yi-Tao Lin, Jian-Wen Qiu, Mei Yu Xu and Bing Peng Xing.