New spiny ostracod species documented in two ancient lakes in southwestern China

A taxonomic study has described Limnocythere curvispinosa sp. nov., a new species of ostracod recovered from living material in Fuxian Lake and from fossil valves in sediments of Yangzong Lake in Yunnan Province, southwestern China. The study combines observations of modern specimens with a Holocene record from two tectonic lakes, while noting limitations in the fossil record and in the available environmental evidence. Fuxian Lake and Yangzong Lake are ancient tectonic lakes in the western branch of the Xiaojiang Fault zone.

Both were formed no later than the Early Pleistocene and belong hydrologically to the Pearl River Basin. Between October 2021 and May 2025, researchers sampled four sites in Fuxian Lake, seven sites in Yangzong Lake and eight small waterbodies around Yangzong Lake for living ostracods. Shallow substrates and macrophytes were sieved with 180 μm mesh; deeper sediments were collected with corers or grabs.

Two piston cores were drilled in the central part of Yangzong Lake: YZHA reached 14.35 m and covers almost the entire Holocene, while YZHB reached 11.25 m and extends into the Late Pleistocene. Living specimens were dissected for examination of appendages and other internal structures. Valve surfaces and appendages were examined with transmitted-light and scanning electron microscopy.

Fossil valves were extracted from core sediment using peroxide and sodium carbonate solution, followed by sieving and manual sorting. Geometric morphometric analysis compared standardized valve outlines, while measurements documented variation in valve length, height, proportions and the sloping angle of the dorsal margin. Fossil specimens supplied developmental and population information, but the internal anatomy of most fossil material was not available.

The new species has small to intermediate-sized, sub-reniform valves with a posteriorly inclined dorsal margin and reticulate surfaces. Adult and late-juvenile right valves have three prominent, posteriorly curved dorsal spines, generally 20–30 μm long. The left valve usually bears one small, anteriorly curved antero-dorsal spine, although rare specimens had two or lacked the spine.

The species name refers to the curved spines on the right valve. The fifth walking leg is longer than the seventh, the male hemipenis is slender and dagger-shaped with a triangular distal lobe, and the female genital lobes are saddle-shaped. Several characters distinguish L. curvispinosa from related taxa.

Compared with the Australian Limnocythere dorsosicula , its right-valve spines are relatively longer and thicker, it has no more than three, and it possesses the small left-valve antero-dorsal spine. Its antennule has five segments rather than six, its walking-leg proportions differ, and its hemipenis is more slender. Geometric morphometric analysis also distinguished the new species from the stouter L. xinanensis , whose left valve lacks the antero-dorsal spine.

The authors place the new species within the L. stationis group and discuss it as part of a potentially distinct lineage in southwestern China, while the taxonomic history of some related specimens remains uncertain. Valves from 25 core samples spanning about 25,000 calibrated years before present to the present indicated that L. curvispinosa colonized Yangzong Lake no later than 11,580 calibrated years before present, near the beginning of the Holocene. Its recorded abundance remained at no more than 1 valve per gram through the Early and Middle Holocene and most of the Late Holocene.

Abundance increased from 1,138 calibrated years before present, or 812 AD, and exceeded 100 valves per gram between 986 and 1952 AD. The maximum recorded value was 1,087 valves per gram at 66 calibrated years before present, corresponding to 1884 AD. After 1991, abundance was below 10 valves per gram, and only two valves were recovered from the youngest analyzed samples, dated to 2011 and 2017.

Males occurred in five samples within the abundance peak, reaching 20% of the sexable population in the 1952 sample. The authors therefore interpret the Yangzong population as sexually reproducing at least during much of 986–1952. In contrast, only one male was found among 69 late-instar individuals from Fuxian Lake, suggesting predominantly asexual reproduction in that population.

The difference may reflect contrasting environmental stability, but the authors present this as a possible explanation rather than a demonstrated cause. The abundance peak in Yangzong Lake did not coincide with either the Medieval Climate Anomaly or the Little Ice Age. The researchers also refer to reported eutrophication, acidification and heavy-metal pollution during the second half of the 20th century.

These temporal associations do not establish a cause, and the study states that analyses of other aquatic organisms are needed to determine the mechanisms behind the population changes. Modern sampling detected L. curvispinosa at four Fuxian Lake sites, including muddy, vegetation-free habitats at depths of 38, 68 and 77 m. At those sites, measured bottom-water temperatures were 14.3–15.8 °C and electrical conductivity was 323–340 μS cm−1.

The species was not observed in 15 surface samples from the Yangzong Lake area, where researchers recovered 506 living ostracods in total from the lake and nearby small waterbodies. The study’s evidence therefore establishes the species’ modern occurrence in Fuxian Lake and its Holocene fossil record in Yangzong Lake, but does not demonstrate a current presence in Yangzong Lake or identify the environmental processes responsible for its historical population dynamics.

Subject of Research: Taxonomic description and Holocene distribution of a new Limnocythere ostracod species in Yunnan’s ancient lakes

Article Title: Limnocythere curvispinosa sp. nov. ( Crustacea , Ostracoda ) from two ancient lakes in the Xiaojiang Fault zone, Yunnan Province, southwestern China

Article References: Jiang, P., Wang, Q., Ge, D., Xie, M., Duan, L., Fan, J., & Zhai, D. (2025). Limnocythere curvispinosa sp. nov. (Crustacea, Ostracoda) from two ancient lakes in the Xiaojiang Fault zone, Yunnan Province, southwestern China. Zoosystematics and Evolution, 101(4), 2369-2386. https://doi.org/10.3897/zse.101.168416

Image Credits: AI Generated

DOI: 10.3897/zse.101.168416

Keywords: ostracods, new species, Limnocythere, Fuxian Lake, Yangzong Lake, Yunnan China, Holocene sediments, paleontology, geometric morphometrics, aquatic biodiversity, curvispinosa, Crustacea