Panagrolaimus einhardi sp. nov. and two sisters of fortune

ABSTRACT Identifying nematodes to the species level is known to be complicated due to their morphological plasticity and limited number of taxonomically important characters. This is especially apparent in the genus Panagrolaimus , which comprises many cryptic species that are morphologically difficult to distinguish but differ genetically. These roundworms are particularly notable for their adaptation to extreme environments that are inhospitable to many other forms of life. Traditional morphological identification methods often fail at distinguishing genetically divergent populations due to high morphological plasticity in Panagrolaimus , limiting the efficacy of species discovery. High-quality genome assemblies overcome these challenges, offering a comprehensive blueprint of an organism’s genetic structure that can be used for species identification. The analysis of ultra-conserved elements across multiple loci harvested from genome assemblies provides robust phylogenetic resolution. In this study, we integrate genome sequencing, ultra-conserved element analysis, and morphological assessment to identify and describe three novel species: Panagrolaimus einhardi sp. nov., formerly Panagrolaimus sp. ES5 from Germany; Panagrolaimus shuimeiren sp. nov. from the Namib Desert; and Panagrolaimus nebliphilus sp. nov. from the Atacama Desert. P. einhardi sp. nov. is named after Prof. Einhard Schierenberg, a renowned expert in roundworm development and cherished member of the nematode community, who isolated this species himself. All three species originate from different geographical locations, and their respective identification are supported by high-quality genome assemblies from either PacBio HiFi or Oxford Nanopore long-read data. The P. einhardi sp. nov. genome was scaffolded using Hi-C technology, which resulted in a 116 Mb collapsed assembly composed of 44 scaffolds (N50: 28 Mb). P. shuimeiren sp. nov. has an assembly size of 69 Mb with 49 scaffolds and a N50 of 13 Mb. P. nebliphilus sp. nov. assembly is 70 Mb with 24 scaffolds (N50: 13 Mb). The capacity of Panagrolaimus to adapt to extreme environments is driving research into their survival mechanisms, requiring comprehensive genomic resources. By combining morphology and genomics, we can gain a more comprehensive understanding of the rich biological diversity in lineages with numerous cryptic species, such as the Panagrolaimidae, thereby clarifying relationships where morphological data alone are ambiguous or confounded.