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A new species of troglomorphic trechine beetle from the karst region of Okinawa's main island accidentally discovered by local researchers


Postdoctoral Researcher Showtaro Kakizoe of the National Museum of Nature and Science, in collaboration with Kazuki Sugaya of Bioindicator Co., Ltd., Sohei Ooka of Nanto Inc., Hisao Tamura of the Asian Bat Research Institute, and Shinzaburo Sone of the Japan Plant Protection Association, has announced that the Trechina beetles found in a cave in the karst area of the Motobu Peninsula in the main island of Okinawa in Japan, have been described as a new genus and new species, Ryukyuaphaenops pulcherrimus gen. & sp. nov. The average length of the beetles is approximately 6.9 mm (from the tip of the chin to the tip of the abdomen), making them one of the largest Trechina species living in Japan. The study findings were published on December 11 in the international academic journal Acta Entomologica Musei Nationalis Pragae.

Ryukyuaphaenops pulcherrimus, the newly discovered species.
Image courtesy of the National Museum of Nature and Science, photo by Showtaro Kakizoe

The Trechina are insects that inhabit underground crevices and cave environments. To date, 380 species in 21 genera have been identified in Japan, in areas from Hokkaido to Kyushu.

Many of them have morphologies not seen in terrestrial insects, such as degenerated compound eyes and hind wings, lack of body pigmentation, and long legs and antennae adapted to underground life.

This new genus and species of trechine beetle was accidentally discovered by Ooka in December 2021 in a vertical pit in the karst area of Motobu Peninsula. Subsequent taxonomic studies conducted by Kakizoe and Sugaya revealed that it belongs to a taxon called Trechina. Its morphology is completely different from that of previously known Trechina species. Therefore, it was named Ryukyuaphaenops pulcherrimus gen. & sp. nov. This is the first time that a Trechina species has been found in the Ryukyu Archipelago. This has greatly expanded the distribution range of Trechina species in Japan to the south.

Ryukyuaphaenops pulcherrimus gen. & sp. nov. was also found to be very similar to a Trechina species existing in caves in the Yangtze River basin in Hubei Province, China, approximately 1,700 km away from Okinawa Island.

Locations of the habitat of the new species and the Motobu Peninsula, Okinawa Island, Japan.
Image courtesy of the National Museum of Nature and Science

Ryukyuaphaenops pulcherrimus gen. & sp. nov. differs morphologically from most other Trechina species in Japan, in that the longitudinal groove on the dorsal surface of the head is absent from the center to the base of the head. It has extremely elongated legs and antennae that, at first glance, resemble those of a spider.

These so-called "troglomorphic" features indicate a particularly strong tendency toward morphological change, a phenomenon observed in organisms adapted to underground environments. Ryukyuaphaenops pulcherrimus gen. & sp. nov. is a typical troglomorphic beetle and one of the most specialized insects for underground environments in Japan.

Kakizoe said, "This discovery by Ooka and Tamura, both of whom live on the main island of Okinawa, is one of the discoveries of the century. Although it was known that troglomorphic Trechina species, which are extremely specialized for underground environments, inhabit continents such as China and Europe, I never dreamed that they would be found in Japan."

"This species was difficult to study because its morphology was completely different from those of the Trechina species found in Japan and Taiwan to date. However, through careful examination of the literature and specimens in our collection, mainly by Sugaya and myself, it became clear that it was similar to the Trechina species in China. We hope to use this discovery as an opportunity to reveal the biodiversity that lies beneath the Ryukyu Archipelago. We also hope to clarify the relationship between the Trechina species in Japan and those around the world from a DNA perspective."

Journal Information
Publication: Acta Entomologica Musei Nationalis Pragae
Title: Discovery of a troglomorphic trechine beetle from the Ryukyu Archipelago, Southwestern Japan (Coleoptera: Carabidae: Trechinae)
DOI: 10.37520/aemnp.2023.020

This article has been translated by JST with permission from The Science News Ltd. ( Unauthorized reproduction of the article and photographs is prohibited.

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