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During the expedition POS397 ‘GroMet’ in 2010 the sediments of the Great Meteor Seamount (GMS) plateau were sampled quantitatively for the first time, allowing statistical analysis of the community structure of Harpacticoida and Canuelloida. Analysis of similarity revealed no differences between three geographic regions at family/species level. Analysis of diversity indicated slightly greater diversity in the south, with more species belonging to more genera/families. Dispersal opportunities possibly occurring at the plateau (emergence, erosion, rafting) are discussed. Of 18 investigated families 106 species were identified, but only 5.66% were already scientifically known and widely distributed. Within the investigated families, 37.74% of the species belonged to shallow-water genera, leading to the conclusion that the plateau was once connected to shallow-water habitats, perhaps functioning as a stepping stone, but is now geographically isolated. This isolation is most likely due to seafloor spreading of the Atlantic Ocean and descending of the GMS. On the plateau, six species with wider distribution ranges were present, indicating that species may arrive accidentally, but their means of settlement remains unknown. Comparisons of the identified GMS plateau fauna with that of other seamounts and mid-oceanic islands revealed similar communities at family level, but at species level the GMS shares only one species with the Seine Seamount; all other elevations had more species in common. Hence, the GMS plateau is considered to be isolated regarding benthic Copepoda but may play an important role in meiofaunal species distribution, as it represents a shallow-water habitat within the deep sea.

Meiofauna samples were collected using the multicorer during three FS POLARSTERN research expeditions to the Southern Ocean between 2013 and 2019. The samples yielded, among other representatives of the CopepodaHarpacticoida, 11 individuals of a previously unknown species of the Ancorabolidae Sars. The six males and five females could be assigned to the genus Conroy-Dalton & Huys, within which they form a separate species. . differs from the two already known species (George) from the Beagle Channel (Chile) and Garlitska, George & Chertoprud from the Barents Sea (Russia) in the following autapomorphies: (i) the female antennule has only nine setae on the last segment instead of ten, (ii) the inner apical seta on P2enp2 is strongly shortened and only reaches half the length of the outer apical seta. In addition to the detailed description of the new species, a morphologically based comparison with the taxa Sars and Conroy-Dalton & Huys confirmed the monophyletic status of . A key to the species is also provided. . has a very limited distribution range. To date, it has only been found on the continental shelf at the northernmost tip of the Antarctic Peninsula and on the continental slope in Bransfield Strait, at depths between 420 and 750 metres. The sediments at the stations where the new species was found were characterised by low bottom temperatures, a high silt and clay content (84-89%), and high pigment content, indicating a high food availability.

Despite the generally recognised importance of CopepodaHarpacticoida in aquatic ecosystems, our knowledge of that taxon is still very patchy and even marginal with regard to deep-sea representatives. Nonetheless, studies over the past decades have shown that deep-sea Harpacticoida present an almost overwhelming diversity of species. In order to obtain a most realistic assessment of this, taxonomic studies are essential in addition to faunistic ones. They reveal that particularly rare deep-sea groups can be characterised by a large number of different species even from the same location. One such rare group is the taxon Dorsiceratus Drzycimski, a representative of the so-called Ceratonotus group (Cletodidae T. Scott). The five species known to date, namely Dorsiceratus dinah George & Plum, Do. octocornis Drzycimski, Do. triarticulatus Coull, Do. ursulae George, and Do. wilhelminae George & Plum, indicate a worldwide distribution of Dorsiceratus . On the one hand, they are characterised by very similar morphological features. Simultaneously, however, derived characters occur very scattered, making a clear characterisation of both the species and a monophylum Dorsiceratus difficult. The aim of the present morphological comparison is to substantiate a monophylum Dorsiceratus and also to characterise the species known to date. For this purpose, we studied Dorsiceratus specimens collected from various marine areas over the past 26 years. The monophyly of Dorsiceratus can be justified by the following autapomorphies: (1) mandibular palpus without basal seta 1, (2) P2enp2 with 1 apical seta, (3) P2exp3 with tube pore, (4) P4 endopod sexually dimorphic. The species can also be characterised by at least one autapomorphy each. Among a total of 57 individuals we studied, we assigned 12 to three new species: Do. andeep sp. nov. , Do. denizae sp. nov. , and Do. karinae sp. nov. , and one male specimen appears to resemble Do. ursulae . However, the remaining 44 individuals could not be morphologically assigned to any of the known or new species. They were provisionally assigned to eight different morphotypes and a heterogeneous morpho-group, which, however, cannot be justified phylogenetically. According to our results, morphological comparison alone is not sufficient for an unambiguous assignment of future findings to Dorsiceratus . It needs to be supplemented by molecular analyses. A diagnostic key to species is provided.

During expedition EMB-238 of RV EM BORGESE to the Fehmarn Belt (Baltic Sea, Germany) in 2020, specimens of a new species of the Rhizothrichidae Por (Crustacea, Copepoda, Harpacticoida) were found. Currently, Rhizothrichidae enclose two genera: Rhizothrix Sars and Tryphoema Monard. The assignment of the new species is based on the following commonly derived characters: the formation of a strong spinulose (sub)apical element on the last segment of the female A1, and the formation of a long brush seta on the last exopodal and endopodal segments of the P1. The new species could not be assigned to either Rhizothrix or Tryphoema because it lacks their autapomorphies but presents exclusive derived characters, including the absence of the abexopodal seta on the A2 allobasis, the possession of only one seta on the endopods of P2–P4, and the fusion of the female P5 exopod and baseoendopod. Therefore, it is assigned to a new genus. Besides the species description, its phylogenetic position in the Rhizothrichidae as well as its possible relationship with Rhizothrix and Tryphoema are discussed. Furthermore, the affiliation of the Rhizothrichidae with the Cletodoidea is justified on the basis of 17 apomorphies. A key to the rhizothrichid genera is provided.

A detailed phylogenetic analysis of the taxon Paralaophontodes Lang ( Copepoda, Harpacticoida, Laophontodinae Lang) based on morphological characters is presented. The monophylum Paralaophontodes is supported by 16 unambiguous autapomorphies such as the presence of characteristic dorsal processes on cephalothorax and body somites, a 5-segmented male antennule, the loss of the syncoxal seta on the maxilliped, and the endopodal strengthening of the first swimming leg. The corresponding extensive phylogenetic evaluation includes the description of Paralaophontodes anjae sp. n. from a beach on Chiloé Island (Chile), the re-description of Laophontodes armatus Lang, and the re-establishment of Paralaophontodes robustus (Bŏzić), the displacement of Laophontodes armatus , L. hedgpethi Lang and L. psammophilus Soyer to Paralaophontodes , a discussion on relationships within that taxon, remarks on its geographical distribution, and a key to the species.

The discovery and description of a new representative of the Ceratonotus group (Copepoda, Harpacticoida, Cletodidae T. Scott) in the Grussaí Canyon off the coast of Brazil opened up the possibility of clarifying the relationship between Echinopsyllus Sars and Pseudechinopsyllus George. Pseudechinopsyllus andrei sp. nov. is characterised by several autapomorphies, including (a) the extensive development of long spinules on the second and third segment of the female antennule, and the strong respectively extreme elongation of (b) the exopod and (c) the setophore on the female P5. Synapomorphies shared with P. sindemarkae include (d) the formation of long spinules at the bases of P2–P4 as well as (e) on exp1 of the P2, and (f) the strong elongation of a tube pore on P2 exp2. Furthermore, the sister group relationship of Pseudechinopsyllus and Echinopsyllus could be substantiated by eleven synapomorphies, among them (g) the large body size, (h) the development of long, rigid cephalothoracic ventrolateral anterior and posterior processes and (i) the loss of the syncoxal seta on the maxilliped. The present study represents a further step towards clarifying the systematic relationships within the Ceratonotus group. A key to the species is provided.

Understanding how meiofaunal communities respond to spatial protection measures is essential for evaluating the effectiveness of marine conservation strategies, particularly in heavily impacted regions such as the Baltic Sea. Here, we present one of the first integrated assessments of meiofaunal diversity across marine protected areas (MPAs) and adjacent reference areas (REFs) in the Baltic Sea. Our study combines whole-community metabarcoding of two genetic markers—mitochondrial COI and ribosomal 18S—with classical morphological identification of harpacticoid copepods. Sampling was conducted in the Fehmarn Belt and Oderbank regions as part of the DAM pilot mission MGF Ostsee, prior to the exclusion of mobile bottom-contact fishing. We provide a valuable baseline of community composition under current conditions. Results highlight strong complementarity between the genetic markers: 18S offered broader taxonomic coverage and higher alpha diversity, particularly for Nematoda and Platyhelminthes, while COI enabled more precise species-level resolution, especially for Copepoda . Spatial analyses revealed distinct assemblages between Fehmarn Belt and Oderbank, with notably higher copepod diversity in Fehmarn Belt. Significant differences between MPAs and REFs were detected only in Oderbank. Morphological and molecular datasets showed substantial but incomplete overlap, with each method capturing unique taxa, demonstrating their combined value for comprehensive biodiversity assessments. Our findings suggest that meiofauna communities reflect both regional environmental gradients and high small-scale patchiness. This study underscores the utility of multi-marker metabarcoding alongside traditional taxonomy for monitoring meiobenthic diversity and highlights the importance of incorporating meiofauna into long-term ecological assessments. The dataset provides a crucial reference point for evaluating future recovery and management outcomes following trawling exclusion.

Seamounts are among the most common physiographic systems in the global deep ocean, defining habitat for a hugely diverse biome. Great Meteor Seamount is located in the subtropical Northeast Atlantic and is considered one of the largest seamounts worldwide. Despite its remoteness, it remains one of the few seamounts globally with a long research history dating back more than 50 years. In this study, we aim to review the recent history of scientific research at Great Meteor Seamount, integrating multidisciplinary datasets of the entire seamount ecosystem, including data on plankton, benthos, fishes, and physical oceanography. The interaction of the seamount topography with background low-frequency and tidal currents creates a unique dynamical response due to its location at the critical latitude for seamount trapped diurnal waves, and the high amplitudes of semidiurnal tides. Biological observations show elevated patchiness on horizontal scales smaller than the seamount, which compares well to other seamounts with shallow summits. Regardless of ecosystem pressures associated with geographic isolation and the nutrient and organic matter deprivation inside the North Atlantic Subtropical Gyre, Great Meteor Seamount hosts a diverse species composition including megafaunal taxa such as sponges and corals, as well as species rich fish populations and meiofaunal groups of copepods and nematodes. Due to the ecological vulnerability of seamount habitats to unsustainable exploitation and their important role as open ocean hotspots of marine life, the Portuguese government plans to designate Great Meteor Seamount as a Marine Protected Area (MPA) under the European Marine Strategy Framework Directive. Here, we summarize and recount important results from the long history of research at Great Meteor Seamount in the context of present-day challenges and the initiatives to protect vulnerable ecosystems.

Kinorhynchs rarely show a wide distribution pattern, due to their putatively low dispersal capabilities and/or limited sampling efforts. In this study, a new kinorhynch species is described, Echinoderespterus sp. n. , which shows a geographically and bathymetrically wide distribution, occurring on the Karasik Seamount and off the Svalbard Islands (Arctic Ocean), on the Sedlo Seamount (northeast Atlantic Ocean), and on the deep-sea floor off Crete and on the Anaximenes Seamount (Mediterranean Sea), at a depth range of 675–4,403 m. The new species is characterized by a combination of middorsal acicular spines on segments 4–8, laterodorsal tubes on segment 10, lateroventral tubes on segment 5, lateroventral acicular spines on segments 6–9, tufts of long hairs rising from slits in a laterodorsal position on segment 9, truncated tergal extensions on segment 11, and the absence of any type-2 gland cell outlet. The specimens belonging to the populations from the Arctic Ocean, the Sedlo Seamount, and the Mediterranean Sea show morphological variation in the thickness and length of the spines as well as in the presence/absence of ventromedial sensory spots on segment 7. The different populations are regarded as belonging to a single species because of their overlapping variable characters.

The record of a new species of Echinolaophonte Nicholls, 1941 (Copepoda, Harpacticoida, Laophontidae) from Jeju Island (Korea) formed the basis for a detailed and exhaustive phylogenetic revision of the genus. Comparison of all 15 species currently assigned to Echinolaophonte (including the new Korean species) revealed that its current composition cannot be maintained. The phylogenetic relationships within Echinolaophonte were elucidated through the analysis of 135 morphological characters and the inclusion of four outgroups. As a result, four species were removed from Echinolaophonte and placed in two new genera: Parechinolaophonte gen. nov. for E. tropica Ummerkutty, 1970 and Pseudechinolaophonte gen. nov. for E. minuta Cottarelli & Forniz, 1991, E. mordoganensis Kuru, Sönmez & Karaytug, 2019 and E. veniliae Cottarelli, Forniz & Bascherini, 1992. Echinolaophonte longantennata Apostolov, 1990 had to be excluded from the analysis, due to the fragmentary and imprecise description. Accordingly, the phylogenetic relationships of the ten species remaining in Echinolaophonte are clarified. The new Korean species is described as Echinolaophonte musa sp. nov. Furthermore, the subspecies E. armiger f. briani Lang, 1965 is elevated to species rank as E. briani Lang, 1965. A detailed phylogenetic discussion is provided and a key to the species of Echinolaophonte is given.