Oddly-shaped river creature is ‘rare’ new species in China. Take a look
In the vast network of rivers and tributaries that make up the Pearl River Basin in southern China, the water is naturally filtered by living creatures.
Throughout the slow-flowing water, freshwater mussels act as animal engineers, building a thriving ecosystem by processing organic material and nutrients.
“China is a diversity hotspot of freshwater mussels,” researchers said in an April 17 study published in the peer-reviewed journal Zoosystematics and Evolution, but they still remain relatively unstudied in the Pearl River Basin.
Then in 2024, researchers conducted surveys of the water system on the hunt for freshwater mussels — and discovered a new species.
“We discovered a group of freshwater mussel specimens with the special expanded posterior that did not resemble any known species and were challenging to place in any genus,” researchers said.
A genus is a group of closely related species, meaning this species not only had not been described in the scientific record, but it was a representative for an entirely new group.
The genus was named Guiunio, a combination of the word “Gui” as an abbreviation for the Guangxi region where it was found, and “unio” from the larger family of mussels of which the new species belongs, according to the study.
The shell of the mussel is “medium-sized, moderately thick, flat, long, sub-glossy (and) opaque,” researchers said.
One end, the anterior side, is “small, rounded and short,” according to the study, but the other end, or posterior side, is “extremely expanded, wide and long,” a feature that sets it apart from other known species.
The mussel was given the species name “rarus” after the Latin word for rare, researchers said, “referring to the rarity of it.”
Guiunio rarus, or the rare Guangxi freshwater mussel, was found “living in the slow flowing stream with muddy and sandy bottom” alongside other species, according to the study.
The mussels were also found with a “yet-to-be-described” species of Rhodeus, a group of fish known as bitterlings, researchers said.
The fish is believed to lay eggs in the gills of the freshwater mussels, but the mussels were collected during the dry season when no eggs were visible, according to the study.
This is a common behavior for bitterlings, and the fish have adapted to have females lay their eggs in the gills of freshwater mussels before the males come along to fertilize them, according to the U.S. Fish and Wildlife Service. The eggs grow to maturity and then leave the mussels. In exchange, the fish will help the mussel get rid of parasites.
“The distribution of both the new species and a yet-to-be-described species of Rhodeus is confined to the same river, representing the second documented instance of sympatric occurrence between a new freshwater mussel and a new bitterling,” researchers said. “Southern China is a hotspot for the both freshwater mussels and bitterlings, and the special mutually beneficial symbiotic relationship between them may have driven their coevolution.”
Guangxi is on the south-central coast of China.
The research team includes Yu-Ting Dai, Zhong-Guang Chen, Fan Li, Xiao-Chen Huang, Shan Ouyang and Xiao-Ping Wu.
This story was originally published April 21, 2025 at 5:20 PM with the headline "Oddly-shaped river creature is ‘rare’ new species in China. Take a look."
