The genus Geophilus is no ordinary group of animals. It is the oldest described genus of soil centipedes, first recognized by Linnaeus in 1758, and today comprises roughly 140 species. Over the centuries, many centipede species were indiscriminately assigned to it because the genus was once defined much more broadly. Subsequent taxonomic revisions have cleaned up some of this confusion, but a full global revision of Geophilus has never been completed. This lingering uncertainty has made it difficult for scientists to resolve how the different species relate to each other, and where the boundaries between species actually lie. The problem is compounded by the fact that most species in the genus have never been sequenced, leaving taxonomists without the molecular data needed to test their hypotheses.

In Romania, eight Geophilus species were listed in the most recent national catalog, with one more described in 2024. Most of these species have wide distributions across Europe or Central Europe, and only one, Geophilus zagreus, was suggested to be a narrow-range endemic restricted to the karst of the Dobrogean plateau. But recent descriptions of small centipede species from other Southeastern European localities hinted that Romania’s true Geophilus diversity was likely underestimated. The lack of coordinated national-scale sampling meant that many small, soil-dwelling species could easily have been overlooked.

That is exactly what happened. The research team, led by George Popovici, Popa, and Iorgu, collected specimens by hand from forests across Romania and stored them in 70% ethanol. They then dissected the animals under light microscopes, drawing every detail of their external anatomy, from the shape of their antennae to the arrangement of pores on their undersides. The two new species, Geophilus captiosus and Geophilus tenuis, were initially so similar to known congeners that they were nearly misidentified. G. captiosus, whose name derives from the Latin for deceptive, was first mistaken for a species of Pachymerium based on superficial characters. G. tenuis, meaning meager or feeble, was recognized for its gracile habitus and small body size.

To confirm that the two new species were genuinely distinct, the researchers sequenced three genetic markers: two nuclear ribosomal genes, 18S and 28S, and one mitochondrial gene, COI. They then constructed the most complete molecular phylogeny of Geophilus ever attempted, including sequence data from every species of the genus present in public repositories. The results were striking. Both new species were recovered as members of a strongly supported monophyletic group that also included the morphologically similar G. flavus and G. zagreus. This clade was recovered despite the geographic isolation and habitat differences between the type localities of these species, which span the Southern Carpathians, the Wallachian Plain, and the Dobrogean karst.

The researchers also employed three molecular species delimitation tools, ASAP, bPTP, and GMYC, to explore the extent of possible cryptic diversity within Geophilus. All three methods identified a larger number of candidate species than the number suggested by morphology alone. The analyses suggested that G. impressus, G. flavus, and G. truncorum each likely contain multiple species hidden under a single name. In the case of G. impressus, sequences assigned to this species were partitioned into at least five candidate species. G. flavus, which is widespread across Europe, showed high genetic variability, with at least three lineages consistently recovered. The researchers used a molecular diagnosis method called MOLD to identify diagnostic nucleotide combinations in the COI barcode region, providing formal DNA-based diagnoses for the new species and their congeners.

The two new species were found in remarkably different habitats. G. captiosus was collected in Carpathian mixed beech and fir forest at an altitude of 1086 meters, while G. tenuis was found in xerothermophilous oak forest at only 90 to 100 meters above sea level. Both species were recorded from leaf litter, under stones, inside rotten wood, and within the upper soil layers. This spatial distribution contrasts with syntopic G. electricus, which is only recorded from within the soil itself. The type locality of G. captiosus is considered among the most intensively sampled sites for centipedes in Romania, yet the species had never been collected there before, suggesting that even well-studied areas may harbor undiscovered diversity.

The discovery of these two species raises important questions about convergence in Southeastern European Geophilus. The researchers note that the geographically proximate and morphologically similar G. serbicus was not recovered in the same clade as the new Romanian species, which are instead closely related to the troglobiont G. zagreus. This tentatively suggests possible convergence on small-sized oligopodous ecomorphs among Southeastern European species. The association of certain characters, such as reduced body size, fewer leg-bearing segments, and the presence of unconsolidated carpophagus structures, with miniaturization could mean that similarities between distant species reflect similar ecological pressures rather than close kinship.

The broader implications of this work extend well beyond Romania. The researchers highlight that the extent of undescribed species diversity in Geophilus is likely substantial, and that comprehensive sampling of small endogeic members of the genus is urgently needed. Patchy distribution data for geophilomorph species across Southeastern Europe represents a major challenge for clarifying the status of poorly known taxa. The region is emerging as a hotspot of Geophilus species diversity, but without systematic surveys of suitable microhabitats, many species may go unnoticed. The two new species described here are a reminder that even in well-explored continents, the smallest inhabitants of the soil can still surprise us, and that the frontier of biodiversity discovery may lie just beneath our feet.

Subject of Research: Integrative taxonomy uncovers hidden diversity in Romanian Geophilus Leach, 1814 (Geophilomorpha, Geophilidae)

Article Title: Integrative taxonomy uncovers hidden diversity in Romanian Geophilus Leach, 1814 ( Geophilomorpha , Geophilidae )

Article References: Popovici, G., Popa, O. P., & Iorgu, E. I. (2026). Integrative taxonomy uncovers hidden diversity in Romanian Geophilus Leach, 1814 (Geophilomorpha, Geophilidae). Zoosystematics and Evolution, 102(2), 533-555. https://doi.org/10.3897/zse.102.177928

Image Credits: AI Generated

DOI: 10.3897/zse.102.177928

Keywords: Integrative, taxonomy, uncovers, hidden, diversity, Romanian, Geophilus, Leach, Geophilomorpha, Geophilidae, scientific research