On December 25, 2025, a research team led by Professor Atsuko Yamaguchi and researcher Keisuke Furumitsu at Nagasaki University revealed that Japan's most familiar coastal ray, the "red stingray" (Akaei), had actually comprised multiple species confused as one for over 160 years.

Through this research, a cryptic species (a species difficult to distinguish due to its similar appearance) primarily found in the Ariake Sea was formally described as the new species "Ariake Red Stingray" (Hemitrygon ariakensis).

The Story Begins in Edo-Period Japan

The classification history of the red stingray traces back to Japan's Edo period. Philipp Franz von Siebold arrived in Nagasaki's Dejima island in 1823 as a physician attached to the Dutch trading post. During his stay, he enthusiastically collected specimens of Japan's flora and fauna.

Based on six stingray specimens collected by Siebold and others and sent to the Royal Dutch Museum (now Naturalis Biodiversity Center), German zoologists Johannes Müller and Jakob Henle described the "red stingray" as a new species in 1841. At the time, all specimens appeared so similar that they were assumed to be the same species.

Over Two Decades of Painstaking Research

The Nagasaki University research team began their taxonomic study of red stingrays in 2003. Their investigation was sparked by noticing populations in the Ariake Sea with subtly different characteristics from conventional red stingrays.

In 2010, they revealed the existence of a cryptic species and proposed the Japanese name "Ariake Akaei" (Ariake Red Stingray), but could not determine its scientific name. This was because they discovered that the original 1841 description was based on specimens containing multiple species.

The research team traveled to the Naturalis Biodiversity Center in the Netherlands to directly examine specimens nearly 180 years old. Their investigation confirmed that the seven type specimens indeed contained multiple species. Furthermore, they found that the lectotype (the specimen designated as the standard for the scientific name) was a juvenile whose morphological features were difficult to distinguish.

How to Tell the Two Species Apart

After years of research, distinguishing features between the two species were identified.

Characteristics of the Ariake Red Stingray

  • The ventral skin fold on the tail is black with white edges
  • A transverse groove exists near the fifth gill slit on the ventral side

These features are difficult to identify without expertise, making it nearly impossible for ordinary beachgoers to distinguish between the species when encountered in the wild.

The Ariake Red Stingray Was Already in the Glover Atlas

Intriguingly, examination of the historical "Fish Atlas of Southern and Western Japan" (commonly known as the Glover Atlas) held in Nagasaki University Library revealed that the only illustration labeled as "red stingray" was actually the Ariake Red Stingray.

The Glover Atlas is a meticulously crafted collection of 806 fish illustrations compiled by Thomas Albert Glover (Japanese name: Tomisaburo Kuraba), son of Scottish merchant Thomas Blake Glover, from the late Meiji era through early Showa period. The fact that the Ariake Red Stingray was already documented in this resource, counted among Japan's "Four Great Fish Atlases", proves this species has inhabited Japanese waters since ancient times.

Significance of the Discovery

This discovery extends far beyond merely resolving a taxonomic issue. Now that we know what was lumped together as "red stingray" actually comprises multiple species, accurate assessment of each species' ecology, distribution, and population becomes possible.

Red stingrays are not only consumed as food but are also popular exhibits at aquariums. They also play important ecological roles as predators of bottom-dwelling organisms in marine ecosystems.

The research paper has been published in the international journal Ichthyological Research and is scheduled for inclusion in Vol.73 No.3 (2026). The holotype (the single specimen that serves as the standard for the scientific name) for the new Ariake Red Stingray was designated as a specimen collected off Shimabara in the Ariake Sea, Nagasaki Prefecture.

This discovery, that an "unfamiliar" species had been hiding in plain sight among "familiar marine creatures" for over 160 years, teaches us that mysteries of biodiversity still exist all around us waiting to be solved.

Have there been discoveries in your country or region where creatures long thought to be the same species turned out to be multiple species? We'd love to hear about the hidden biodiversity in your local environment!

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