[Okayama University] New Subspecies of Oncomelania Found on Iriomote Island - No Concerns About Schistosomiasis Japonica!

This is a joint research press release from Okayama University and Dokkyo Medical University.

March 30, 2026 National University Corporation Okayama University

https://www.okayama-u.ac.jp/

・ A new subspecies of Oncomelania, widely known as the intermediate host for Schistosomiasis japonica, was discovered at a waterfall in the mountains of Iriomote Island, Okinawa Prefecture, and has been officially described and named as *Oncomelania hupensis iriomotensis*.

・ Infection experiments with Schistosomiasis japonica and environmental DNA analysis of the site yielded no evidence indicating a risk of infection.

・ The distribution of this new subspecies is extremely limited, qualifying it as Critically Endangered IA under the Ministry of the Environment's Red List criteria, necessitating strong conservation measures.

◆Overview

A joint research group comprising Associate Professor Hiroshi Fukuda from the Faculty of Environmental and Life Science (Agriculture), Okayama University (Headquarters: Kita-ku, Okayama City, President: Yasuo Tajima), Project Researcher Naoto Sawada from the Graduate School of Science, The University of Tokyo, and Lecturer Masashi Kirinoki from the Graduate School of Medicine, Dokkyo Medical University, has discovered an unknown species of freshwater snail in a mountain waterfall on Iriomote Island, Okinawa Prefecture. They have identified it as a new subspecies of *Oncomelania* (Katayama snail) and officially described it as *Oncomelania hupensis iriomotensis* Fukuda & Sawada in Sawada, Kirinoki & Fukuda, 2026.

While *Oncomelania hupensis* found in Honshu and Kyushu are intermediate hosts for Schistosomiasis japonica and have caused severe damage to human health, infection experiments with this new subspecies and environmental DNA analysis of its habitat have not yielded data indicating an infection risk. However, further research is necessary to assess potential risks.

Unlike *Oncomelania hupensis*, which is found in lowlands such as around rice paddies, the new subspecies is exclusively found around waterfalls, a significant difference. Due to its extremely limited distribution, it is considered critically endangered and requires conservation measures.

These research findings were published on February 11, 2026, in the American malacological journal "*Malacologia*.".

This information was released by Okayama University on March 23, 2026.

Shell of the new subspecies *Oncomelania hupensis iriomotensis*. A is the holotype.