The northward distribution limit of groundwater fauna is generally dictated by the extent of glacial ice sheets during the Pleistocene. However, some taxa can be found far above this limit, sometimes on isolated oceanic islands, implying long-term survival in subglacial subterranean refugia. Here we report a peculiar assemblage comprising two new depigmented and blind (stygomorphic) amphipods from the subarctic ancient lake El’gygytgyn (northern Far East): Palearcticarellus hyperboreus sp. nov. and Pseudocrangonyx elgygytgynicus sp. nov. Molecular phylogenetic analyses based on five markers confirm their affinity to Crangonyctidae and Pseudocrangonyctidae, respectively. Fossil-calibrated molecular dating indicates that the ages of both species predate the onset of Pleistocene glaciations by at least an order of magnitude. Although both species are clearly adapted for subterranean life and are related to groundwater taxa, they are only known from the lake waters (5–170-m depth). Despite being nested within Pseudocrangonyctidae, P. elgygytgynicus has an atypical third uropod that preserves a vestigial inner ramus, a trait characteristic to the monotypic sister family Crymostygidae. Given that this character was the main distinguishing feature between the two families, we propose merging Crymostygidae with Pseudocrangonyctidae. Our findings represent the world’s northernmost record of stygomorphic amphipods, emphasising their relictual biogeography and the importance of Lake El’gygytgyn as a long-term, high latitude refugium for ancient pre-glacial fauna.

ZooBank: urn:lsid:zoobank.org:pub:3A51D1F8-E65D-4A3A-B663-D5C40272E68B

Recent studies have proposed different biogeographic patterns of intertidal Diaulota and marine littoral Psammostiba along the Pacific coasts of the Northern Hemisphere. To compare the biogeographic patterns of different lineages of aleocharine beetles and explore the recurrent patterns among them, we studied coastal Adota, with a distribution range almost identical to those of Diaulota and Psammostiba. We performed phylogenetic analysis of the marine littoral Adota occurring on the Pacific coasts of the Northern Hemisphere using molecular characters (5188 bp: ~1452 bp of COI, ~404 bp of COII, ~475 bp of 16S, ~879 bp of 18S, ~973 bp of 28S, ~542 bp of EF1-α and ~463 bp of Wg) to discuss their phylogenetic relationships and biogeographic patterns. The data were analysed using parsimony (PA), Bayesian (BA) and maximum likelihood (ML) methods. The genus Adota and clade A with the same patterns of relationships (A. sinanensis ((A. elongata + A. koreana) (A. magnipennis + A. ushio))), were strongly supported as monophyletic in all analyses. The PA, BA and ML analyses yielded different species relationships in clade B: (A. kamchatkaensis (A. namhae + A. maritima)) in the ML tree using IQ-TREE2, (A. namhae (A. kamchatkaensis + A. maritima)) in the BA and RAxML trees and unresolved polytomy in the PA tree. Our results suggest that the ancestors of Adota were widespread along the East Asian coasts (North and South Korea, Japan, and Kamchatka, Russia). Subsequently, Adota species expanded their range and underwent vicariance between South Korea and Japan and Russia (Kamchatka). Later, another dispersal event occurred from South Korea and Japan to North America and a vicariance event occurred between South Korea and Japan, and North America. Adota have similar biogeographical patterns to Psammostiba, probably because they occupy the same microhabitats and have similar biological characteristics. The findings demonstrate the importance of microhabitats and biological traits in the study of biogeographic patterns of marine coastal insects.

Freshwater bivalves (Bivalvia, Unionida, Unionidae) are among the most threatened groups of animals in the world. Taxonomic uncertainties pose a particular challenge due to significant intraspecific variation and apparent plasticity in shell morphology among these species, impeding efficient conservation planning and management. The species Unio szechenyii that is endemic to China has long been regarded as a synonym for Cuneopsis heudei due to the high convergence in shell morphology. The recently validated species Middendorffinaia mongolica is currently restricted to the Amur Basin and Primorye in eastern Russia. This species is classified under the tribe Middendorffinaiini of the subfamily Unioninae within the family Unionidae based on multilocus phylogeny. However, the lack of comprehensive taxonomic information and sufficient molecular phylogenetic data casts uncertainty on the validity and taxonomic status of these two species. We aim to reassess the validity of Unio szechenyii and confirm the taxonomic status of Middendorffinaia mongolica, a new record for China, by integrating taxonomy with robust mitochondrial phylogenomics. We support the validity of Unio szechenyii and propose a recombination as Cuneopsis szechenyii comb. nov. by integrating shell morphometry, soft-body anatomy and molecular evidence. By determination of the mitochondrial genome of Cuneopsis szechenyii, Cuneopsis kiangsiensis, Middendorffinaia mongolica and Pseudocuneopsis wuana, we elucidate intrageneric relationships within the genera Cuneopsis and Pseudocuneopsis. In addition, based on the updated consensus taxonomic framework including tribes and subtribes in Unioninae, mitochondrial phylogenomics strongly support the transfer of Middendorffinaia mongolica from the tribe Middendorffinaiini to the tribe Unionini and classification under the subtribe Middendorffinaiina stat. rev.

ZooBank: urn:lsid:zoobank.org:pub:820589D5-0100-4195-B92B-1E1005384B9B