The lack of regular monitoring actions associated with high costs and long-lasting taxonomic expertise prevents the environmental assessment and implementation of conservation strategies in many regions of the World Ocean, especially in the tropical Large Marine Ecosystems, like the Gulf of Guinea, a basin influenced by numerous anthropogenic threats associated with oil excavation, and at the same time, very scarcely studied. Our study aimed to compare the effectiveness of the standard monitoring protocols based on Van Veen grab samples, with video recordings obtained using a Remotely Operated Vehicle (ROV) along the coast of Ghana in the 250–1000 m depth gradient. We have applied a variety of multivariate methods and diversity measures to analyse responses of benthic communities to multiple environmental factors of natural and anthropogenic origin. Even though both gears collect completely different faunas and pointed at possible sampling bias associated with specific features of each sampling gear, the analysis allowed to detect the same most important disturbance agents, like barium and hydrocarbons. The ROV material allowed for relatively quick taxonomic analysis and provided a reliable dataset allowing to obtained results of efficiency and reliability comparable to grab samples that are more effort-consuming for the taxonomic analysis.

Background:Despite centuries of exploration, marine invertebrate biodiversity remains notably under-described. The majority of species in major marine groups are still unnamed, limiting our ability to understand and conserve ecosystems facing rapid environmental change. The rate of species discovery continues to outpace the formal process of species description. This gap creates an urgent need for streamlined, scalable approaches to taxonomy. The SENCKENBERG OCEAN SPECIES ALLIANCE was founded to help meet this challenge by facilitating global collaboration, offering technical support for species documentation and promoting efficient taxonomic publishing. Within this framework, Ocean Species Discoveries provides a forum for concise, but data-rich descriptions of marine invertebrate taxa. This second collection presents a diverse set of taxonomic contributions, based on recent and historical collections, including newly-described species and a re-description of a previously poorly-known taxon. The integrative documentation of the taxa treated herein was facilitated by the newly-established Discovery Laboratory at the Senckenberg Research Institute, the first service unit dedicated to supporting alpha taxonomists. New information:This article presents 14 new species and one re-description, two new genera, with taxa spanning three phyla. Newly-described taxa comprise two polychaete annelids: Nicon salinus Hernández-Alcántara & Dávila-Jiménez, sp. nov. and Spinther bohnorum Tilic & Rouse, sp. nov. Molluscs span four classes, with three polyplacophorans: Craspedochiton zefranki Vončina, sp. nov., Ferreiraella charazata Sigwart, sp. nov. and a new genus with type species Pycnodontochiton sinensis Sirenko, Zhang & Sigwart, gen. et sp. nov. and Pycnodontochiton tenuidontus (Saito and Okutani, 1990), comb. nov. The new monoplacophoran Veleropilina gretchenae Sigwart & Steger, sp. nov. is one of the first species of this class with a high-quality genome, published from the specimen that is now the holotype. The scaphopod Laevidentalium wiesei Sahlmann, 2012 represents a re-description and range extension and the bivalve Myonera aleutiana Machado & Sigwart, sp. nov. is the second bivalve including an anatomical description with non-invasive methods using micro-CT. Amongst crustaceans, there are two new amphipod species: Apotectonia senckenbergae Momtazi & Riehl, sp. nov. and Metharpinia hirsuta Souza-Filho & Andrade, sp. nov. Three isopod species were described, including the parasitic species Zeaione everta Boyko & Williams, sp. nov. that is the only species in the new genus Zeaione Boyko & Williams, gen. nov. and two free-living isopods: Haploniscus bulbosus Henseler, Knauber & Riehl, sp. nov. and Macrostylis peteri Riehl, sp. nov. Finally, there are two new tanaidaceans: Hoplopolemius olo Jóźwiak & Stępień, sp. nov. and Nesotanais thalassinus Stępień, sp. nov.The data used for the description of ten of the species and one of the new genera treated herein were wholly or partially obtained at the SOSA Discovery Laboratory using integrative methods including light and electron microscopy, confocal imaging, molecular barcoding and micro-CT scanning. Additional novel findings include the first record of the family Macrostylidae and the genus Macrostylis G. O. Sars, 1864 from Australian waters (Macrostylis peteri, sp. nov.) and novel host associations: Ferreiraella charazata, sp. nov. is documented with epibiotic tubeworms on its tail valves that are typical of this genus and the decapod Eucalliaxiopsis aequimana (Baker, 1907) is newly recorded as a host for bopyrid isopods, representing the first such record for the family Eucalliacidae.

Human-driven environmental changes in the ocean are reshaping the diversity and distribution of coastal organisms. Understanding species diversity is essential for assessing threats, predicting impacts, and guiding conservation planning. Our study focuses on the family Leptocheliidae (Crustacea: Tanaidacea), a suitable model for investigating diversity and distribution in low-mobility crustaceans. This family, abundant in shallow waters and sensitive to environmental shifts, was analyzed at global scale using literature, databases, and unpublished data from Australian coral reefs. Species richness, estimated richness, and sampling effort were calculated organizing data into latitudinal bands and ca. 800,000 km hexagonal cells. Cluster analysis by biogeographic provinces was used to identify distinct species assemblages Generalized Linear and Additive Models (GLM, GAM) assessed environmental drivers, including temperature, productivity, chlorophyll, dissolved oxygen, salinity, silicate, phytoplankton, nitrate, and phosphate. Results revealed a bimodal species richness pattern, with diversity peaking in lower latitudes and declining at the equator. Biodiversity hotspots were identified in the Indo-Australian region, central Indo-Pacific, Gulf of Mexico, and Caribbean, with high estimated richness in the Mediterranean and SE Australia. The subpolar region displayed distinct, but low-diversity assemblages. Among the environmental variables, dissolved oxygen was identified as the most important factor influencing species diversity and estimated diversity across latitudes, followed by temperature. Models incorporating salinity were the most reliable for species diversity within hexagonal regions.

Biological invasion and introduction of non-native species pose a major threat in the twenty-first century. Latest studies indicate that small, low mobile Crustacea, like Peracarida, are a major component of the fouling community. At the same time, they are usually neglected in monitoring due to their small size and problems with identification. Growing evidence of cryptic invasions encourages us to look closer at one of the most abundant components of peracarid assemblages in fouling communities – the Tanaididae (Tanaidacea). Prior findings on the possible invasiveness of the family are scarce. In the literature and databases only five species have been indicated as invasive. Herein, we propose a multisource approach to verifying the distribution of Tanaididae and estimating the risk of cryptic invasion by its members. We review the available data on Tanaididae occurrence, affinities to anthropogenic habitats and molecular data from global databases and literature. As a result, we have identified 24 species of Tanaididae as having invasion potential, and a further 30 species with affinities to anthropogenic habitats, that might be sources of cryptic invasions in the future. Moreover, our comprehensive study allowed us to identify seven species with conflicting information around distribution or taxonomy that may lead to misidentification.

The Mediterranean Sea is recognized as one of the most threatened marine environments due to pollution, the unintentional spread of invasive species, and habitat destruction. Understanding the biodiversity patterns within this sea is crucial for effective resource management and conservation planning. During a research cruise aimed at assessing biodiversity near desalination plants in the vicinity of Larnaca, Cyprus, conducted as part of the WATER-MINING project (Horizon 2020), specimens of the tanaidacean genus Apseudopsis were collected. These were classified into two species, identified as new to science, and are described herein as Apseudopsis larnacensis sp. nov and Apseudopsis salinus sp. nov. Apseudopsis larnacensis sp. nov is distinguished from its congeners by the presence of a lateral apophysis on pleonite 5, which is longer than those on pleonites 1-4, hyposphenia on pereonites 2-6, and six ventral spines on the propodus of pereopod 1. Apseudopsis salinus sp. nov. is characterized by a rounded posterolateral margin on pereonite 6, hyposphenia on pereonites 1-6, and four ventral spines on the propodus of pereopod 1. An updated key to the Atlantic and Mediterranean Apseudopsis species is provided. This study provides an overview of the distribution, bathymetric, and habitat preference of all known Apseudopsis species. Data extracted from the literature and two popular online databases were analyzed to identify diversity patterns across seas and ecoregions. Our analysis reveals that the Mediterranean is the most diverse region for Apseudopsis, with the Levantine Sea hosting ten species and the South European Atlantic Shelf seven species. Shallow waters and muddy and sandy habitats are conducive for Apseudopsis occurrence.

Current environmental changes due to increased human activities are impacting biodiversity and distribution of marine organisms. Understanding species diversity is essential for assessing threats, predicting impacts, and guiding conservation planning. Our study focuses on the family Leptocheliidae (Crustacea: Tanaidacea), a suitable model for investigating diversity and distribution in low-mobility crustaceans. This family, abundant in shallow waters and sensitive to environmental shifts, was analyzed globally using literature, databases, and unpublished data from Australian coral reefs. We calculated species richness, estimated richness, and sampling effort, organizing data into latitudinal bands and ca. 800,000 km2 hexagonal cells. Cluster analysis by biogeographic provinces helped identify distinct species assemblages. Generalized Linear and Additive Models (GLM, GAM) assessed environmental drivers, including temperature, productivity, chlorophyll, dissolved oxygen, salinity, silicate, phytoplankton, nitrate, and phosphate. Results revealed a bimodal species richness pattern, with diversity peaking in lower latitudes but declining at the equator. Biodiversity hotspots were identified in the Indo-Australian region, Central Indo-Pacific, Gulf of Mexico, and Caribbean, with high estimated richness in the Mediterranean, and SE Australia. The subantarctic region displayed distinct, but low-diversity assemblages. Among the environmental variables, dissolved oxygen was identified as the most important factor influencing species diversity and estimated diversity across latitudes, followed by temperature. Models incorporating salinity, combinations of multiple factors, and dissolved oxygen were the most reliable for species diversity within hexagonal regions, while combinations of several environmental factors, followed by temperature, were the best predictors for estimated diversity.

A major challenge in invasion science is detecting overlooked introductions, their pathways of introduction and spread. One of the most successful introduced taxa in aquatic ecosystems are peracarid crustaceans. There are a growing number of reports of accidental introductions of peracarids worldwide, mostly related to human transport hubs (e.g., ports and marinas). Tanaidaceans are especially abundant in these communities. Most frequently given examples of natural and anthropogenic passive dispersers belong to the family Tanaididae. However, their wide distribution requires confirmation. Most records come from 70–80’ of last century, when identification of the species relied only on morphological characters. The small size and large intraspecific variation of tanaidids generate a high taxonomic uncertainty, as in the case of Zeuxo turkensis . Population of this species was previously known from Turkish, Japanese, and Australian coasts. In the two last places this tanaidid was identified as Hexapleomera sasuke , despite there were some premises that it should be synonymized with Z. turkensis . Here we investigate specimens that resembled both Hexapleomera sasuke and Zeuxo turkensis collected in marinas around the Iberian and Moroccan coasts. Integrating morphological and molecular methods (barcoding) we confirmed: (1) the first record and presence of well-structured populations of Z. turkensis in Spain, Portugal and Morocco, representing the first record of the species for Atlantic waters; (2) the conspecificity between H. sasuke and Z. turkensis , which should be synonymized; and (3) the wide distribution of Z. turkensis associated with human transport hubs (i.e. marinas) in the study area, showing its potential for introduction and spread. Integrated approaches and greater taxonomic support are key to advancing knowledge on the origin and invasion patterns of this and other small and poorly known human-mediated widespread species.

Agathotanais is one of the seven genera classified into the family Agathotanaidae. So far, 12 species have been described for the genus, seven of which are known from the Pacific. However, considering the present poor state of knowledge on deep-sea environments, a much higher number of Agathotanais species than currently known can be suspected. Among the studied material, collected from below 1,000 m during five deep-sea expeditions in different parts of the Pacific Ocean, we identified eight species: two of them were already known to the science and five species were identified as new to knowledge and their formal description is presented in the paper: two from the North West Pacific (the Sea of Okhotsk and Kuril-Kamchatka Trench), two from the Central Pacific (Clarion-Clipperton Fracture Zone), and one from the Australian slope. The eighth Agathotanais species in our material was determined using a molecular approach, but it was represented by only one partially destroyed individual and could therefore not be formally described. The proportion of Agathotanais collected at the Sea of Okhotsk was the highest (22%), whereas the numbers were substantially lower for the Kuril-Kamchatka Trench, and the Central and the Southern Pacific. Molecular analyses confirmed the monophyly of Agathotanais and Paragathotanais and a close relationship between both genera. Moreover, a close relationship between the two Australian species was revealed. As a result of our findings, the number of species known from the Pacific increased from 5 to 11, with the total number of species in this genus increasing from 12 to 17. An updated identification key for Agathotanais species is given.

The Gulf of Guinea is characterised by a complex hydrology and supports a high species diversity. A recent study has indicated that the area can be considered a refuge for rare taxa. Intensive sampling off the coast of Ghana (Gulf of Guinea) in 2012 on board the R/V F. Nansen resulted in the discovery of a large number of benthic invertebrates, including peracarid crustaceans. A preliminary investigation demonstrated a high diversity of the Cumacea, with 95% of the species being new to science. The most species-rich genus was Eocuma with seven species; six of them proved new to science and are described here. Additionally, the global distribution of Eocuma was analysed with the help of a phylogenetic tree based on morphological characters, Bayesian Binary Markov chain Monte Carlo biogeographic analysis and literature data. The radiation centres of the west African fauna are discussed.

A new family of paratanaoidean Tanaidacea, the hamatipedids, formerly part of the Typhlotanaidae, is established to accommodate three genera ( Hamatipeda and two new). Deep-sea hamatipedids collected from four sites in the Atlantic (Argentine and Guiana basins) and 14 sites from the Southeast coast of Australia were studied using a taxonomic approach combining morphological and morphometric data. Four new species of Hamatipeda and one of a new genus are described from different deep-sea areas of the Atlantic and Pacific oceans. Hamatipeda sima originally classified within Hamatipeda , is transferred to a new genus. We observed that several morphometric characters (i.e., length of the last two pereonites) in different life-stages of one of the new Hamatipeda species (neuter, manca-2, and manca-3) are correlated with the total body length (TBL). Applying a morphometric approach, we aimed: (1) to identify those ontogenetic-dependent characters, and (2) to detect the characters, which can be used in discrimination of Hamatipedidae species, regardless their life-stage.

The Gulf of Guinea belongs to the most scarcely sampled marine basins in the oceans of the world. We have analyzed diversity and distribution patterns of cumacean communities on the shelf and slope, along the coast of Ghana. The material was collected in October and November of 2012 using a van Veen grab (0.1 m2) on nine transects. Six stations were located at each transect (25, 50, 100, 250, 500, and 1,000 m). Sixty-three species of Cumacea were recorded with Leucon and Eocuma as the most speciose genera, with 12 and eight species, respectively. Comparisons of species richness with literature data pointed that the Ghanaian coast hosts very diverse communities. About 95% of species were new to science, and the number of cumacean species known from the West Africa increased by over 100%. Nevertheless, most of the species had extremely low abundance, 13 singletons and 15 doubletons were found. Mean density of cumaceans was estimated at only 1.5 ind./0.1 m2. Species accumulation curve did not reach the asymptotic level, suggesting undersampling, despite the fact that sampling effort was high (250 samples). The highest species richness was recorded in the inner shelf (25–50 m) and on the slope (1,000 m). Cluster analysis separated shallow water communities from deeper regions on the shelf and upper slope. The most unique species composition was found at 1,000 m. Principal component analysis showed the importance of oxygen, sediments, and human-related disturbance for distribution of cumacean communities. In the shallows, oxygen content and presence of gravel were the most important factors structuring communities. In the deeper bottom areas (250–1,000 m), cumacean fauna was affected by local pollution, mainly by higher concentration of barium, other heavy metals, and THC.

The Great Barrier Reef (GBR) is considered to be one of the most important marine biodiversity hotspots on Earth. At the same time, knowledge on the smallest inhabitants of this habitat is extremely scarce, which is particularly apparent with respect to small peracarid crustaceans of the order Tanaidacea. Prior to this study, as few as 20 tanaidacean species had been reported from Australian coral reefs, this study yielding 56 species new to science. Our analysis of a high number of qualitative samples collected at two GBR sites (Heron and Lizard Islands) from a depth range of 0 to about 30 m in the framework of the Census of Coral Reef Ecosystem program (one of the Census of Marine Life-related projects) almost doubled the total number of coral reef-associated tanaidacean species known worldwide. Altogether, 60 species (distributed among 7622 individuals) were identified, 46 and 41 species being recorded on Heron and Lizard Islands, respectively. The tanaidaceans were dominated by members of the families Leptocheliidae (8 species and more than half of all specimens at both sites) and Metapseudidae (11 species, 6 and 3% of individuals, respectively). The most speciose genera were Pseudoapseudomorpha (4 species), Paradoxapseudes, Parapseudes, Pugiodactylus, and Zeuxo (3 species each). Most species were rare, their frequency of occurrence in samples not exceeding 15%. The species accumulation curves did not reach the asymptote.

The Sea of Okhotsk is one of the world's largest marginal seas; its benthic fauna, especially from deeper parts, remains virtually unexplored. The material for this study was collected in the Sea of Okhotsk, Bussol Strait, and from the northern slope of the Kuril-Kamchatka Trench, during the Russian-German expedition Sea of Okhotsk Biodiversity Studies (SokhoBio) onboard the RV Akademik M.A. Lavrentyev in 2015. Material was collected using a camera-equipped epibenthic sledge (C-EBS). Forty-six tanaidacean species representing 31 genera and 12 families were found in 19 samples collected at depths from 1696 to 4798 m. All the species were new to science. The highest number of species (44) was recorded in the deepest part of the Sea of Okhotsk (Kuril Basin), followed by the northern slope of the Kuril-Kamchatka Trench (16 species) and the Bussol Strait (3 species). Almost one-third of all tanaidaceans (14 species) were common to both sides of the Kuril Island archipelago. Our results reveal a substantial faunal exchange between those two areas, although the small number of samples makes final conclusions about faunal similarity between the Sea of Okhotsk and the Pacific Ocean not fully possible. The level of rarity and patchiness of the tanaidacean fauna was high. The large number of species and individuals per sample observed in the Sea of Okhotsk might reflect high food availability in this area.

The halocyprid ostracod genus Boroecia Poulsen, 1973 is described in detail and Boroecia borealis (Sars, 1866) is nominated as type species. We unravel several taxonomic confusions and uncertainties in the earlier literature that had their origins in the classification of Boroecia maxima and Boroecia antipoda (Müller, 1906) as subspecies of Boroecia borealis. Three new species are described, B. alaska n. sp., and B. danae n. sp. from the Pacific and B. hopcrofti n. sp. from the high Arctic, bringing the total number of species in the genus to six. Five of the species are described in detail, the only exception is Boroecia maxima (Brady Norman, 1896), for which there is already a full description in the literature. Comparative illustrations are provided for all the species together with standardised meristic data. A key to the identity all six species is included.

During two IceAGE expeditions, a large collection of Tanaidacea was gathered from the shelf down to the slope (213−2750 m) in six areas off Iceland—the Irminger Basin, the Iceland Basin, the Norwegian Sea, the Denmark Strait, the Iceland-Faroe Ridge, and the Norwegian Channel. In this collection, members of the family Pseudotanaidae were most numerous component. We examined 40 samples collected with different gears (e.g., EBS, VVG. GKG), in which 323 pseudotanaid individuals were counted and covered a total depth from 213.9 to 2746.4 m. Morphological identification of the material has revealed the presence of five species: Akanthinotanais cf. longipes, Mystriocentrus biho sp. n. Pseudotanais misericorde sp. n., P. svavarssoni sp. n., and P. sigrunis sp. n. The description of the four new species has been presented in the paper and a rank of the subgenus Akanthinotanais is elevated to a genus rank. A large group of morphologically almost identical specimens, similar with P. svavarssoni sp. n. from a wide depth range and from various areas off Iceland was discriminated to species by applying morphometric methods; one distinct species (P. svavarssoni sp. n.) and complex of presumably cryptic species the species was discovered. Based on current data and literature records, similarity among fauna of Pseudotanaidae was assessed with applying Bray–Curtis formula. As results, potential zoogeographic regions in the North Atlantic have been distinguished.

The tanaidacean metapseudid subfamily Synapseudinae Guţu is reviewed, partially revised and the type species, Synapseudes minutus Miller, redescribed. As rediagnosed and defined here, the Synapseudinae is restricted to the genera Synapseudes Miller, Vicinisyndes Guţu, and Creefs Stępień Błażewicz-Paszkowycz. The genera Curtipleon Băcescu and Cryptapseudes Băcescu are excluded from this subfamily. Three new species, S. caleyi, S. singularis, and S. hansknechti are described, bringing the number of putative species within the genus to 26. An identification key and table of selected specific characters for the species of Synapseudes are provided. A new monotypic genus, Ronabus, which is placed within the subfamily Metapseudinae Lang, is erected to receive Synapseudes idios Gardiner. The present taxonomic status of subfamilies within the Metapseudidae is briefly assessed.

Body size is one of the most important biological characters, as it defines many aspects of organismal functioning at the individual and community level. As body size controls many ecological aspects of species, it is often used as a proxy for the status of the ecosystem. So far no consistent mechanism driving size shift has been proposed. In this study, we investigated bathymetric variability in zooid’s size and shape in aquatic colonial animals, Bryozoa. Although the response of bryozoan zooid size to temperature or food concentration has been experimentally proven, the effects of natural environmental variability on marine bryozoan populations has been much less explored. The presented investigation is aimed to assess the bathymetric patterns and environmental drivers of bryozoan zooid size on continental shelf and slope of southern Iceland. 196 colonies of 11 species representing different colonial forms and taxonomic groups were selected for zooid characteristics measurements. A pattern of depth-related increase in zooid size was documented for Bicellarina alderi, Chartella barleei and Sarsiflustra abyssicola, no statistically significant effects were detected for the other eight species. Two species Bicellarina alderi and Caberea ellisii had significantly longer zooids in deeper water, shape of the remaining species did not change along the bathymetric gradient. Intercolonial coefficient of variation in zooid size did not change across the depth gradient. Temperature differences along studied depth could be responsible for the observed pattern.

Discoconchoecia elegans (Sars, 1865) is one of the most frequently recorded species of halocyprid ostracods and specimens are collected in abundance from various latitudes throughout the world oceans. This species is often dominant or subdominant member of the mesopelagic assemblages. However, its body size varies substantially with latitude, posing the question as to whether D. elegans is either a single, highly variable species, or a complex of cryptic and sibling species. Evaluation of the hypothesis that D. elegans is a complex of species requires comparison between the type material and specimens collected from different latitudes. The inadequacy of the original description from the type locality, off the Lofoten Islands (NW Norway), combined with a lack of the type material is preventing critical rating. In this paper Discoconchoecia elegans is redescribed from specimens collected from an area close to Svalbard, using detailed drawings, morphometric measurements of all limbs, and SEM photographs, and it is compared with specimens collected from an area close to the species type locality. The individuals from those two localities show no significant differences, probably because the hydrographic conditions are similar between the two sites.