A new genus and two new species of terrestrial crustaceans described from Georgian caves
A 4 mm, colourless, eyeless crustacean from two caves in Upper Imereti turned out to be so distinct that it got a new genus, Imeretioniscus. A second new species, Colchidoniscus fissus, was described from caves in Odishi.
Researchers from the Institute of Zoology at Ilia State University, together with an Italian colleague, studied five species of terrestrial isopods (Isopoda) that live in Georgian caves. Two of them are new to science, and one needed a new genus of its own: Imeretioniscus. The paper was published in Zootaxa on 8 April 2026.
Small crustaceans that live in the dark
Many people remember the woodlice they found under a stone. These are terrestrial isopods: crustaceans that left the water and live on land. Some of them went further still, into the darkness of caves.
The new paper is about such animals. All five species of the subfamily Haplophthalminae (family Trichoniscidae) found in Georgian caves are troglobionts. That means they live only underground. Their bodies are colourless, they have no eyes at all, and none of them reaches 5 millimetres.
The authors are Stefano Taiti of the Research Institute on Terrestrial Ecosystems of Italy's National Research Council, and Lado Shavadze, Eter Maghradze and Shalva Barjadze of the Institute of Zoology at Ilia State University. The specimens were collected in 19 caves in western Georgia between 2017 and 2023.
Imeretioniscus: a genus with three ridges on its back
The new genus has one species, Imeretioniscus tricostatus. It was found in two caves on the Upper Imereti Plateau, in Chiatura municipality: Sadatviaklde and Shvilobisa. The two caves lie on opposite banks of the Kvirila River, about 12 kilometres apart. The type specimen, a male, was collected in Sadatviaklde by Lado Shavadze on 11 August 2023.
Males reach 4 mm and females 3.5 mm. The genus is named after Imereti, and the species name comes from the Latin tricostatus, "three-ribbed". Each body segment carries three large ridges on its back: one in the middle and one on each side.
According to the authors, this sets it clearly apart from every other genus of Haplophthalminae. A midline bump is found in only one other genus, the Italian Sanfilippia, known from a single species in two caves in Liguria, northwestern Italy. It has only one bump per segment, not three ridges.
Colchidoniscus fissus: from the caves of Odishi
The second new species, Colchidoniscus fissus, belongs to an already known genus. It was found in three caves in Samegrelo, in Chkhorotsku municipality: Abano and Garakha caves on the Odishi plain and Shurubumu Cave on the Migaria karst massif. The type specimen was collected in Abano Cave on 25 September 2020.
Males reach 3 mm and females 4 mm. The Latin fissus means "split". The large bump on the third abdominal segment has a tip divided in two. This, and the structure of the male's legs, sets it apart from its close relative, Colchidoniscus kutaissianus.
A subspecies that turned out to be a species
These Georgian cave crustaceans were first described in 1974. At that time, Colchidoniscus kutaissianus was split into two subspecies. New material from Motena Cave showed that the two differ enough. The authors therefore recognised the Motena form as a separate species: Colchidoniscus motenae.
C. motenae differs in its wider body, the size of the bumps on its head and the ridges on the last body segment, which sit close together. It is known only from Motena Cave, on the Askhi karst massif in Martvili municipality.
Five species, several of them from a single cave
The most widespread is Colchidoniscus kutaissianus. It is endemic to western Georgia and was found in many caves of the Sataplia–Tskaltubo karst massif, including Prometheus, Satsurblia and Solkota. Other records come from Khoni, Chkhorotsku and Verdzistava II Cave on the Khvamli massif in Racha-Lechkhumi.
The other species have much smaller worlds. Mingrelloniscus inchhuricus is known only from Inchkhuri Cave near Martvili, and C. motenae only from Motena. Imeretioniscus tricostatus was found in two caves, C. fissus in three. The paper also includes a key to all five species, which leads from a specimen's characters to its name.
The type specimens are kept at the Natural History Museum of the University of Florence, and part of the remaining material at the Institute of Zoology of Ilia State University.
What remains to be resolved
The authors themselves point to one open question. The back ornamentation of Colchidoniscus closely resembles that of two genera from Italy, Switzerland, Austria and the northern Balkans. A comparison with them, including a genetic one, will be important to confirm that the genus stands on its own.
One thing is already clear: of the five species, two are known from a single cave, and two more from two or three caves. If you visit a cave in western Georgia, walk carefully: there may be an animal underfoot that science knows from that one place only.
