Eurythenes gryllus is one of the most widespread amphipod species, occurring in every ocean with a depth range covering the bathyal, abyssal and hadal zones. Previous studies, however, indicated the existence of several genetically and morphologically divergent lineages, questioning the assumption of its cosmopolitan and eurybathic distribution. For the first time, its genetic diversity was explored at the global scale (Arctic, Atlantic, Pacific and Southern oceans) by analyzing nuclear (28S rDNA) and mitochondrial (COI, 16S rDNA) sequence data using various species delimitation methods in a phylogeographic context. Nine putative species-level clades were identified within E. gryllus. A clear distinction was observed between samples collected at bathyal versus abyssal depths, with a genetic break occurring around 3,000 m. Two bathyal and two abyssal lineages showed a widespread distribution, while five other abyssal lineages each seemed to be restricted to a single ocean basin. The observed higher diversity in the abyss compared to the bathyal zone stands in contrast to the depth-differentiation hypothesis. Our results indicate that, despite the more uniform environment of the abyss and its presumed lack of obvious isolating barriers, abyssal populations might be more likely to show population differentiation and undergo speciation events than previously assumed. Potential factors influencing species’ origins and distributions, such as hydrostatic pressure, are discussed. In addition, morphological findings coincided with the molecular clades. Of all specimens available for examination, those of the bipolar bathyal clade seemed the most similar to the ‘true’ E. gryllus. We present the first molecular evidence for a bipolar distribution in a macro-benthic deep-sea organism.

Because of the unique conditions that exist around the Antarctic continent, Southern Ocean (SO) ecosystems are very susceptible to the growing impact of global climate change and other anthropogenic influences. Consequently, there is an urgent need to understand how SO marine life will cope with expected future changes in the environment. Studies of Antarctic organisms have shown that individual species and higher taxa display different degrees of sensitivity to environmental shifts, making it difficult to predict overall community or ecosystem responses. This emphasizes the need for an improved understanding of the Antarctic benthic ecosystem response to global climate change using a multitaxon approach with consideration of different levels of biological organization. Here, we provide a synthesis of the ability of five important Antarctic benthic taxa (Foraminifera, Nematoda, Amphipoda, Isopoda, and Echinoidea) to cope with changes in the environment (temperature, pH, ice cover, ice scouring, food quantity, and quality) that are linked to climatic changes. Responses from individual to the taxon‐specific community level to these drivers will vary with taxon but will include local species extinctions, invasions of warmer‐water species, shifts in diversity, dominance, and trophic group composition, all with likely consequences for ecosystem functioning. Limitations in our current knowledge and understanding of climate change effects on the different levels are discussed.

Summary: 1. Reliable assessments of groundwater biodiversity are urgently needed to resolve current issues relating to the protection of aquifers. The assessment of groundwater biodiversity is hampered by the physical complexity and difficult access to the subterranean environment, which is related to the vastness, high degree of fragmentation and environmental heterogeneity of groundwater systems. Knowledge on groundwater biodiversity is also biased towards penetrable karstic habitats (caves), whereas other common habitats such as those found in porous aquifers have been neglected. This situation calls for a standardised and comprehensive strategy to sample an exhaustive and balanced set of groundwater habitats.2. A standardised sampling protocol aimed at capturing the main sources of environmental heterogeneity within regions was applied in six regions across Europe. Four hierarchical levels were considered: (i) region (c. 400 km²); (ii) basin (c. 100 km²); (iii) aquifer type (karstic or porous) and (iv) habitat (hyporheic and phreatic zones for porous aquifers; saturated and unsaturated zones for karst aquifers). A total of 192 sampling sites equally distributed among habitats were sampled within each region.3. Stygobiotic species richness significantly varied across regions, probably as a result of important difference in physical and biogeographical characteristics among the regions. Only one species (Graeteriella unisetigera) occurred in all six regions, underlining the narrow geographic range and high degree of endemism of stygobiotic fauna. The low frequency of occurrence of stygobionts also points to the importance of rarity in ground waters and its relevance for drawing up sampling designs.4. Rarefaction curves were calculated to determine sampling efficiencies within each region. Despite the high sampling effort, the curves did not reach saturation, especially in the Cantabria, Lessinia and Krim regions, which had the greatest numbers of rare species.5. Species accumulation curves were also calculated by considering the main sources of environmental heterogeneity among basins, aquifer types and habitats captured by the sampling protocol. In two regions (Roussillon and Jura) sampling efficiency was improved by considering several basins, aquifers and habitats. In the other regions the effect of environmental heterogeneity among basins was low, or absent, but efficiency was higher in the Lessinia and Krim regions when considering both kinds of aquifers and all four habitats. In Cantabria and Wallonia, possible improvement would be expected only when sampling effort is increased or other sources of environmental heterogeneity are integrated.6. General recommendations to refine the sampling strategy thus include identification of sources of environmental heterogeneity such as latitude, altitude, anthropogenic disturbances and regional history. Optimal hydrologic conditions during sampling are an important prerequisite for reliable assessments of groundwater biodiversity and repeated sampling is necessary if this requirement is not met.

The purpose of our contribution is to propose a robust and practical order-level classification of the families of Oligochaeta, that is, non-leech Clitellata. The order level is mandatory in Linnaean rank-based classification and is also required in many internet-based biodiversity databases. However, it has received little attention in oligochaete systematics, and the few available order-level classifications of Oligochaeta no longer represent phylogenetic relationships adequately. Our proposal is based on corroborated molecular phylogenetic evidence and takes as benchmarks class level for Clitellata, subclass level for Oligochaeta and Hirudinea, and order level for Crassiclitellata, the monophylum that includes most of the earthworm taxa. As a result, eleven orders are proposed: Alluroidida Timm & Martin, 2015; Capilloventrida Timm, n. ordo; Crassiclitellata Jamieson, 1988; Enchytraeida Kasprzak, 1984; Haplotaxida Brinkhurst & Jamieson, 1971; Lumbriculida Brinkhurst & Jamieson, 1971; Moniligastrida Brinkhurst & Jamieson, 1971; Narapida Timm, n. ordo; Parvidrilida Timm, n. ordo; Randiellida Jamieson, 1988; Tubificida Jamieson, 1978. This order-level classification is robust and easily adaptable to future insights into phylogenetic relationships.