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 study also redescribed Hemitrygon akajei, the species long known simply as the red stingray, covering how its features change with growth stage and sex.

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 Dutch National Museum of Natural History (now the 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.

In 2013, Yamaguchi traveled to the Naturalis Biodiversity Center in the Netherlands to examine specimens nearly 180 years old. Seven specimens had been stored there as a single species: the six used in the 1841 description plus one added by later work. Close study showed at least three species among them. Five were taxidermy mounts that could not be identified to species, while the lectotype (the specimen designated as the standard for the scientific name) and one closely similar specimen were both juveniles taken off Nagasaki.

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

Even specialists find these hard to read, so a beachgoer meeting one in the shallows has little chance of telling them apart.

The Ariake Red Stingray Was Already in the Glover Atlas

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 more than 800 fish illustrations compiled by Tomisaburo Kuraba, also known as Thomas Albert Glover, son of the Scottish merchant Thomas Blake Glover, from the late Meiji era through the early Showa period. That the Ariake Red Stingray already appears in this atlas, counted among Japan's "Four Great Fish Atlases", indicates the species has long inhabited Japanese waters.

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 paper by Keisuke Furumitsu and Atsuko Yamaguchi appeared in the early online edition of Ichthyological Research, the English-language journal of the Ichthyological Society of Japan, on December 19, 2025, and was carried 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.

A species went unrecognized for over 160 years inside Japan's most ordinary ray. Even familiar waters still hold creatures without names.

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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