Osegi
Science·2 min read

New peanut worm species found in Japan's deep sea has saw-toothed hooks

Two new peanut worm species from Japan's deep sea carry tiny hooks lined with saw-like teeth, a shape never seen in the group before. They were hiding in old samples.

A small deep-sea peanut worm with a tiny hook at its front end, lined with fine saw-like teeth.
Image: ギズモード・ジャパン
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Two newly described deep-sea peanut worms from Japan have a feature nobody had seen in the group before: a tiny hook at the front of the body with a edge like a saw blade.

Peanut worms (hoshimushi in Japanese) are soft, worm-like animals related to earthworms and ragworms. A team from the University of the Ryukyus, the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and other institutions announced on November 9 that they had identified two new species. They are called Nokogiri-samehada-hoshimushi (the saw-skinned peanut worm) and Myojin-samehada-hoshimushi.

Under magnification, the hook on each worm is covered in rows of fine projections that look like saw teeth. Some peanut worms already have hooks, but this many projections in a row had not been confirmed before. The hooks are thought to help gather food. Why these two species have saw-shaped ones is still unknown.

How were the new peanut worms discovered?

Not on a fresh dive. The team went back to specimens collected between 1999 and 2011 and kept in storage. Differences in body features and DNA showed they were new species.

The saw-hooked worm was found near a hydrothermal vent field off the Ogasawara Islands and around a whale carcass that sank off Nomamisaki in Kagoshima Prefecture. The Myojin species came from a vent field off the Izu Islands and from a spot on the seafloor off the southwest islands where methane seeps out.

Life without sunlight

In the dark deep sea, microbes that live on chemicals such as hydrogen sulfide and methane support the animals around them. Sunken whales and sunken wood create similar oases, scattered across the seabed.

The team also used DNA analysis to estimate when the ancestors of these worms moved onto sunken wood and animal remains: about 109 million years ago, within a wide range of 62 to 162 million years. Whales did not exist then. The researchers say the ancestors may have used sunken wood or the carcasses of marine reptiles such as plesiosaurs, and then spread to vents from there.

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Tags:peanut wormdeep seanew speciesjapanjamstechydrothermal vent

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