The Scotia Arc and Amundsen Sea are contrasting regions within West Antarctica. The Scotia Sea shelf is well studied and central to the origin and diversity of the Southern Ocean benthic fauna, whilst the shelf of Amundsen Sea is one of the least studied shelf areas in the world; a 'white spot' on the map of benthic research. Here we report on the tanaidaceans collected using an epibenthic sledge on two expeditions, BIOPEARL 1 and 2, of the RRS James Clark Ross in 2006 and 2008, respectively. This study represents the first analysis of the tanaidacean fauna of those two basins. Thirty-seven species were found in the Amundsen Sea from 500-1500 m depth and 51 species were found at depths ranging from 200-1600 m in the Scotia Sea. In the Scotia Sea, many species were unique to each of the study sites which may be evidence of allopatric speciation episodes. Site specificity was especially evident for Typhlotanais and Pseudotanais. Only three species were common to both basins. Around 90% of the species were previously undescribed. Our findings increase the number of the tanaidaceans known in the Southern Ocean by 50%.

Tanaidaceans belong to the most severely underestimated groups of benthic macrofauna of the Southern Ocean. Here, we analyze 11 samples collected with a small-meshed epibenthic sled in the summer season of 2008, in the Ross Sea, at the shelf break, slope and abyss (365-3490 m). The material was obtained during a RV Tangaroa voyage as part of the New Zealand International Polar Year, Census of Antarctic Marine Life Project. Seventy-two species of Tanaidacea were recorded, 85 % of which were new to science. The most speciose genera are Typhlotanais, Pseudotanais and Paraleptognathia. Rare species (singletons and doubletons) constituted 60 % of the material. Each of the three studied depth zones was characterized by a unique tanaidacean fauna. Only few species (\6 %) occurred consistently in more than one depth zone. The highest number of species (31 species) was recorded in the abyssal sites, and the lowest number of species (20 species) at the shelf sites.

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The benthic fauna associated with polymetallic nodule fields is scarcely studied. Studies on species richness and distribution patterns are indispensable for the conservation of the abyssal ecosystem and for the development of management strategies for sustained commercial activities in the future. Here, we analysed the distribution patterns and diversity of tanaidacean communities associated with four International Seabed Authority licenced areas (BGR, IOM, GSR, Ifremer) located in the Clarion-Clipperton Fracture Zone (North-East equatorial Pacific) and the one Area of Particular Environmental Interests (APEI3). The study was based on 34 box core samples collected at depths ranging from 4,200 to 5,000 m. Altogether, 98 species (446 individuals) were recorded, of which 47 were singletons. Most tanaidaceans (78 species) were unique to a specific area. The highest densities, species richness and diversity were recorded in the BGR license area, while the lowest values were found in the APEI3. Our results correspond to the differences in productivity observed among the five areas. Species accumulation curves demonstrated substantial undersampling, and the final conclusions about tanaidaceans diversity in the CCFZ should be treated with caution, requiring further studies with higher sampling effort. The extremely low densities (2.3 ± 2.3 ind./0.25 m2) and species richness (five species) recorded in the APEI3 suggest a need for the revision of planned conservations strategies in the CCFZ, although it was the most scarcely sampled area and our results are therefore not representative of the entire site. Highlights ► First large scale quantitative assessment of tanaidacean communities associated with polymetallic nodule fields. ► Unique species composition associated with different licence areas of the Clarion Clipperton Fracture Zone. ► Very low diversity and abundance of tanaidaceans in the Area of Particular Environmental Interests (APEI3)

A new family of paratanaoidean Tanaidacea – Paranarthrurellidae fam. nov. – is erected to accommodate two genera without family classification (Paratanaoidea incertae sedis), namely Armatognathia Kudinova-Pasternak, 1987 and Paranarthrurella Lang, 1971. Seven new species of Paranarthrurella and two of Armatognathia are described from material taken in different deep-sea areas of the Atlantic and Pacific oceans. The type species of Paranarthrurella — P. caudata (Kudinova-Pasternak, 1965) — is redescribed based on the paratype. The genus Cheliasetosatanais Larsen and Araújo-Silva, 2014 originally classified within Colletteidae is synonymised with Paranarthrurella, and Arthrura shiinoi Kudinova-Pasternak, 1973 is transferred to Armatognathia. Amended diagnoses of Armatognathia and Paranarthrurella genera are given. Choosing characters for distinguishing and defining both genera was supported by Principal Component Analysis. Designation of the new family is supported by molecular phylogenetic analysis of COI and 18S datasets. The distribution of all species currently included in the new family was visualised and their bathymetric distribution analysed.