The family Eumunididae constitutes an ideal taxon to study deep-sea diversification processes. It includes 35 species present on continental shelves and slopes with a mainly circumtropical distribution. Here, we pursue to answer three questions: i) Are the subgenera previously proposed by experts valid? ii) What was the role of the closure of the Isthmus of Panama in eumunidid’s evolutionary history? iii) Is there variation in the diversification rate (speciation and extinction rates) among lineages? To answer these questions, we reconstructed a time-calibrated phylogeny of Eumunididae, including more than 60% of the known species diversity, using genomic data (Ultraconserved elements, UCEs). We identified ancestral areas of diversification and used Dispersal-Extinction Cladogenesis (DEC) + J model and Bayesian Analysis of Macroevolutionary Mixtures (BAMM) to estimate the ancestral range of lineages and their diversification rate. Our systematics results revealed cryptic species, disputed the validity of Pseudomunida, and although there was strong phylogenetic signal for the character diagnosing the subgenera, Eumunida was rendered polyphyletic. Our data furthermore indicated a relatively recent, rapid diversification of the family during the Late Miocene. Atlantic lineages are more closely related to the eastern Pacific lineages than to the Indian Ocean lineages, and vicariance resulting from the formation of the Isthmus of Panama caused eastern Pacific-western Atlantic diversification. Our results highlight that combining dense taxonomic sampling with the analysis of genomic data fundamentally improves our understanding of the evolutionary history and current patterns of diversity in a deep-sea biogeographic framework.

Our phylogenetic and taxonomic study demonstrates that the genus Galathea originated during the Late Jurassic-Cretaceous, within the Tethyan realm, which is supported by the fossil record. Initially, the genus diversified into two main lineages: one comprising exclusively Atlantic species, including the largest members of the genus (Galathea strigosa and Galathea squamifera), and another consisting of small-sized species that also occurred in this region but diversified widely in the Indian and Pacific Oceans prior to the Cenozoic closure of the Tethys. Furthermore, this integrative study, combining morphological and molecular data, confirms the existence of 16 valid species in the Atlantic. These results resolve long-standing taxonomic uncertainties and clarify previously debated species boundaries, such as those involving Galathea bolivari, Galathea cenarroi, and Galathea intermedia. Our results support the recognition of cryptic species within what were previously considered single taxa. Accordingly, we propose the resurrection of two historical synonyms: Galathea glabra and Galathea parroceli, for species formerly grouped under G. squamifera and G. intermedia, respectively. Morphological characters useful for distinguishing species have been validated, including the shape of the rostrum, the number and size of the ridges, and the structure of the setae on the carapace and pleon.

Even though it is one of the most studied marine regions in the world, the biodiversity of the Mediterranean Sea is still incompletely characterised. In this study, we explore the taxonomy and evolutionary history of the porcelain crab genus Pisidia in the Atlanto-Mediterranean Province, where it has undergone a complex taxonomic history resulting in identification confusion and synonymisation. Through an integrated study using a multilocus phylogeny based on two mitochondrial genes and three nuclear genes, haplotype networks, alongside a morphological analysis and 3-D renderings of micro-CT X-ray images, we investigate the diversification patterns of species complexes in the region. As a result, we have identified five distinct lineages that correspond to presumed species of Pisidia in the eastern Atlantic and the Mediterranean, each well-differentiated by both molecular and morphological characteristics. Our time-divergence analyses suggest that interspecific diversification occurred during the Miocene, whereas intraspecific diversification took place during the Pleistocene. Paleoclimatic and paleogeographic events, such as the Messinian Salinity Crisis and the Pleistocene glacial cycles, played a significant role in the evolution of Pisidia in the Mediterranean and East Atlantic. Additionally, we found species sympatry in several locations in the western Mediterranean, which may explain the long-standing taxonomic debate arising from the coexistence of morphologically distinct species that were previously assumed to be conspecific.

Seamounts are vulnerable ecosystems targeted by fishing and potentially by future mineral exploitation. Their abundance, widespread distribution, and heterogeneity of faunal and abiotic components require integrated studies at multiscale to describe spatial patterns and identify environmental drivers needed by conservation plans. There is also a lack of knowledge on seamount benthic ecosystems in some regions, such as the Indian Ocean. These gaps, in the context of Marine Protected Areas establishment in the region, have motivated the present study focusing on the Mozambique Channel Eparses islands and flat top seamounts, along a 10-degree latitude gradient. These structures are characterized by complex volcanic and carbonate geomorphologies at multiscale and are distributed along a highly dynamic turbulent ocean circulation area with large anticyclonic eddies. For the first time, we analysed, from seabed image transects obtained by towed-camera on four seamounts, and two volcanic islands - Bassas da India and Mayotte - external slopes, and from multiscale environmental data, how benthic communities respond to this high habitat heterogeneity at regional, and local scales. This study reveals high discrepancies of benthic megafauna richness, density, and beta diversity among seamounts and among slopes of the same islands. Moreover, at similar latitude, seamounts display higher densities than island slopes. The highest densities found on a seamount of the Glorieuses archipelago are explained by strong currents and flat homogeneous geomorphology. Except on this seamount, the beta diversity is high, despite the quite limited depth range explored (84-734 m) and is the highest on island slopes and Hall Bank, driven by the diversity and hardness of the substrate. Beta diversity is mainly due to taxa turnover, with high contribution of the habitat-forming sponges and cnidarians, together with a few mobile taxa. We identified from biogeographic network analysis 12 dominant faunal assemblages, displaying a patchy distribution, with variability in composition both among and within sites. Currents and primary productivity explain similar to 15% of the observed assemblage structure along the channel, while geomorphology (km scale), topography (60-500 m scale) and substrate (60-m units) explain together 24% of the faunal spatial patterns. Analysis of spatial structures along island slopes detected some small (100-200 m), medium (similar to 1 km) and large scale (similar to 2-6 km) megabenthic community structures, partly explained by topography, substrate, depth, and slope. Despite limited taxonomic identifications for this poorly sampled area, this study reveals an outstanding heterogeneity of megabenthic assemblages at multispatial scales in the Mozambique Channel seamounts and island slopes, in response to the complex hydrography and geology of the area. Further characterization of environmental drivers with greater focus at local scales including hydrographic variables are therefore needed to improve predictions of suitable habitats of vulnerable marine ecosystems.

Tropical Deep-Sea Benthos, a continuation of Résultats des Campagnes MUSORSTOM, is a series dedicated to the inventory and description of the deep-sea fauna of the world, with special emphasis on the most extensive, yet remote and least explored, region —the Indo-West Pacific. The comprehensive series of marine expeditions undertaken by the French Muséum national d’Histoire naturelle and the Institut de Recherche pour le Développement (IRD) continue to collect many new, strange and sometimes colourful crustaceans. The present volume is the second volume dedicated to Alain Crosnier who passed away on 18 February 2021. Madagascar and more generally the South Western part of the Indian Ocean had a special place in his heart. From 1970 to 1976, he directed the ORSTOM Centre in Nosy Be in Madagascar where he explored the seabed to a depth of more than 1,000 m, thus discovering new resources and new species. The second part of his career was devoted to crustacean systematic and the exploration of the deep benthos of tropical areas. In addition to the deep-sea cruises, which he instigated for a long time, he deployed his visionary energy to organise the study of the collected specimens —by bringing specialists from all over the world to Paris— and to publish these results. In 1999, the “MUSORSTOM cruises” became Tropical Deep-Sea Benthos; the programme celebrated its 40th anniversary in 2016. This second volume is a compilation of two major articles, on crustaceans Chirostylids and corals Stylasterids from South-West Indian Ocean. In this volume, keys to species, descriptions, colour illustrations and drawings, maps and compilation of species occurrences as well as descriptions of new species are provided at regional scale. With a total of 85 new species, i.e. 60 new species of Chirostylids and 25 new species of Stylasterids, this volume provides new knowledge on crustaceans and corals from South West Indian Ocean and conclusions about biogeography in this area are also presented in this volume. Laure Corbari and Magalie Castelin are research-scientist and respectively curators of crustaceans and cnidarians collections of the Muséum national d’Histoire naturelle from Paris.

Leptochela Stimpson (1860) is a shallow-water, benthopelagic genus within the predominantly pelagic superfamily Pasiphaeoidea. We inventoried a global fauna of 17 currently valid species of Leptochela and identified a newly discovered eighteenth species. Our analysis combined both morphological and molecular data, using 13 characters (including two multistate characters) and 5 gene markers, respectively. The results revealed incongruence between the molecular and morphological datasets. However, our phylogenetic conclusions were based on a consensus approach, integrating morphological, molecular, and total evidence trees, which revealed three robust clades. We discuss the evolutionary development of quantitative and qualitative morphological traits in Leptochela and explore the potential causes of the incongruence between morphological and molecular signals, particularly in the context of pelagic eucarids transitioning from pelagic to benthopelagic habitats. Additionally, we describe the new species from Madagascar and provide a key to all known species of Leptochela.

Within the hyper-diverse group of the amphipods, little is known about deep-sea benthic species that still represent an unknown reservoir of species to be discovered, particularly in remote regions of the southwestern Pacific. Herein, we are describing three new deep-sea species of Rhachotropis from Papua New Guinea, Solomon archipelago, and Vanuatu using an integrative taxonomy approach, combining morphological and molecular characters with biological and ecological information. Nomenclatural comments and a key to Rhachotropis species occurring in the bathyal provinces from the southwestern Pacific are also provided. Comments on the sex ratio and fecundity of the genus are also discussed. The biogeography and distribution of the newly described species as well as congeneric species occurring in the area are discussed, and new DNA data are shedding new light on the global phylogenetic relationships (geography, depth range) of the deep-sea genus Rhachotropis.

The phylogeny of sea spiders has been debated for more than a century. Despite several molecular studies in the last twenty years, interfamilial relationships remain uncertain. In the present study, relationships within Pycnogonida are examined in the light of a new dataset composed of 160 mitochondrial genomes (including 152 new sequences) and 130 18S rRNA gene sequences (including 120 new sequences), from 141 sea spider morphospecies representing 26 genera and 9 families. Node congruence between mitochondrial and nuclear markers was analysed to identify the most reliable relationships. We also reanalysed a multilocus dataset previously published and showed that the high percentages of missing data make phylogenetic conclusions difficult and uncertain. Our results support the monophyly of most families currently accepted, except Callipallenidae and Nymphonidae, the monophyly of the superfamilies Ammotheoidea (Ammotheidae + Pallenopsidae), Nymphonoidea (Nymphonidae + Callipallenidae), Phoxichilidioidea (Phoxichilidiidae + Endeidae) and Colossendeoidea (Colossendeidae + Pycnogonidae + Rhynchothoracidae), and the sister-group relationship between Ammotheoidea and Phoxichilidioidea. We discuss the morphological evolution of sea spiders, identifying homoplastic characters and possible synapomorphies. We also discuss the palaeontological and phylogenetic arguments supporting either a radiation of sea spiders prior to Jurassic or a progressive diversification from Ordovician or Cambrian.

We provide an overview of the World Amphipoda Database (WAD), a global species database that is part of the World Register of Marine Species (WoRMS). Launched in 2013, the database contains entries for over 10,500 accepted species names. Edited currently by 31 amphipod taxonomists, following WoRMS priorities, the WAD has at least one editor per major group. All accepted species are checked by the editors, as is the authorship available for all of the names. The higher classification is documented for every species and a type species is recorded for every genus name. This constitutes five of the 13 priorities for completion, set by WoRMS. In 2015, five LifeWatch grants were allocated for WAD activities. These included a general training workshop in 2016, together with data input for the superfamily Lysianassoidea and for a number of non-marine groups. Philanthropy grants in 2019 and 2021 covered more important gaps across the whole group. Further work remains to complete the linking of unaccepted names, original descriptions, and environmental information. Once these tasks are completed, the database will be considered complete for 8 of the 13 priorities, and efforts will continue to input new taxa annually and focus on the remaining priorities, particularly the input of type localities. We give an overview of the current status of the order Amphipoda, providing counts of the number of genera and species within each family belonging to the six suborders currently recognized.

The accurate assignment of cryptic larvae to species-level is a key aspect of marine ecological research and can be achieved through integrated molecular and morphological studies. A combination of two mitochondrial markers (COI and 16S) and a detailed morphological analysis was used to identify phyllosoma larvae of slipper lobster (Scyllaridae) species collected during a survey in the SW Indian Ocean. Two morphotypes were tentatively assigned to Acantharctus ornatus and Biarctus pumilus, both genera for which the larval morphology was unknown. Morphological revision of an adult specimen used to generate the putative A. ornatus sequences in GenBank revealed that it was misidentified and corresponds to B. dubius. The final phyllosoma stage of B. pumilus and subfinal and final stages of A. ornatus were described, clarifying prior misidentifications in the literature. Scyllarid biodiversity in the SW Indian Ocean is underestimated and sampling of deeper water layers is recommended to complete current knowledge of species and larval stages present in the region.

This study presents the inventory of sea spiders (Pycnogonida) sampled during the Madibenthos Expedition in Martinique (West Indies). Species were discriminated leaning on morphological and molecular data. A total of 761 specimens are classified in 72 species, 16 genera and nine families. Thirteen new species are described: Ammothella dirbergi sp. nov., A. krappi sp. nov., Tanystylum boucheti sp. nov., T. ingrallis sp. nov., Ascorhynchus iguanarum sp. nov., Eurycyde kaiouti sp. nov., Nymphon dorlis sp. nov., N. ludovici sp. nov., N. martinicum sp. nov., N. timons sp. nov., Anoplodactylus madibenthos sp. nov., Pycnogonum cesairei sp. nov. and Rhynchothorax sidereus sp. nov. We describe a neotype for Anoplodactylus micros Bourdillon, 1955 from the type locality. Martinique now includes 79 species of sea spiders, mostly endemic to the Tropical Northwestern Atlantic, cosmopolitan or shared with the South America Atlantic coast. Some species are potentially introduced. However, our knowledge of the distribution of species found in Martinique is probably biased by the scarcity of diagnostic morphological characters. Also, nine potentially cryptic species (discriminated on genetic data alone), are identified, shedding light on the overlooked diversity of sea spiders in the Tropical Northwestern Atlantic. Therefore, we call for a more widespread use of barcoding in sea spiders.

The exceptional hidden diversity included in the squat lobster genus Phylladiorhynchus and its wide bathymetric and geographic range make it an interesting group to thoroughly study its evolutionary history. Here we have analyzed the entire currently known species diversity of Phylladiorhynchus using an integrative approach that includes morphological and molecular characters. The aim was to establish whether depth range (bathymetry) has played a role in their morphological and molecular evolution and in their diversification pathways. Phylogenetic analyses recovered the genus as monophyletic and as the sister group of Coralliogalathea, conforming with current systematic hypotheses, although their placement in a monophyletic Galatheidae is doubted. All the analyzed species represent well-supported lineages, structured in ten clades, correlated in most part with the morphological phylogeny. The reconstruction of ancestral habitat showed that the most recent common ancestor of Phylladiorhynchus most likely lived in shallow water environments. The divergence time estimation analyses dated the origin of the genus back to the Upper Jurassic, preceding the origin of all the other galatheoid lineages. Morphological analyses suggested that species from deeper waters exhibit greater morphological divergences and lower genetic divergences in comparison to species from shallower waters. In Phylladiorhynchus, the colonization of deeper waters has taken place independently multiple times since the Lower-Cretaceous. Our reconstruction of ancestral habitat suggests that shallow water ancestors might show an acceleration in the molecular rate of evolution and a slowdown in the rates of morphological evolution in comparison to deep sea lineages. However, although lineages from shallow and deep sea habitats show slight differences in diversification trends, bathymetry does not significantly affect the diversification rate in Phylladiorhynchus according to our diversification analyses.

Imagery has become a key tool for assessing deep-sea megafaunal biodiversity, historically based on physical sampling using fishing gears. Image datasets provide quantitative and repeatable estimates, small-scale spatial patterns and habitat descriptions. However, taxon identification from images is challenging and often relies on morphotypes without considering a taxonomic framework. Taxon identification is particularly challenging in regions where the fauna is poorly known and/or highly diverse. Furthermore, the efficiency of imagery and physical sampling may vary among habitat types. Here, we compared biodiversity metrics (alpha and gamma diversity, composition) based on physical sampling (dredging and trawling) and towed-camera still images (1) along the upper continental slope of Papua New Guinea (sedimented slope with wood-falls, a canyon and cold seeps), and (2) on the outer slopes of the volcanic islands of Mayotte, dominated by hard bottoms. The comparison was done on selected taxa (Pisces, Crustacea, Echinoidea, and Asteroidea), which are good candidates for identification from images. Taxonomic identification ranks obtained for the images varied among these taxa (e.g., family/order for fishes, genus for echinoderms). At these ranks, imagery provided a higher taxonomic richness for hard-bottom and complex habitats, partially explained by the poor performance of trawling on these rough substrates. For the same reason, the gamma diversity of Pisces and Crustacea was also higher from images, but no difference was observed for echinoderms. On soft bottoms, physical sampling provided higher alpha and gamma diversity for fishes and crustaceans, but these differences tended to decrease for crustaceans identified to the species/morphospecies level from images. Physical sampling and imagery were selective against some taxa (e.g., according to size or behavior), therefore providing different facets of biodiversity. In addition, specimens collected at a larger scale facilitated megafauna identification from images. Based on this complementary approach, we propose a robust methodology for image-based faunal identification relying on a taxonomic framework, from collaborative work with taxonomists. An original outcome of this collaborative work is the creation of identification keys dedicated specifically to in situ images and which take into account the state of the taxonomic knowledge for the explored sites.

The ecology, abundance and diversity of galatheoid squat lobsters make them an ideal group to study deep-sea diversification processes. Here, we reconstructed the evolutionary and biogeographic history of Leiogalathea, a genus of circum-tropical deep-sea squat lobsters, in order to compare patterns and processes that have affected shallow-water and deep-sea squat lobster species. We first built a multilocus phylogeny and a calibrated species tree with a relaxed clock using StarBEAST2 to reconstruct evolutionary relationships and divergence times among Leiogalathea species. We used BioGeoBEARS and a DEC model, implemented in RevBayes, to reconstruct ancestral distribution ranges and the biogeographic history of the genus. Our results showed that Leiogalathea is monophyletic and comprises four main lineages; morphological homogeneity is common within and between clades, except in one; the reconstructed ancestral range of the genus is in the Atlantic and Indian oceans (Tethys). They also revealed the divergence of the Atlantic species around 25 million years ago (Ma), intense cladogenesis 15-25 Ma and low levels of speciation over the last 5 million years (Myr). The four Leiogalathea lineages showed similar patterns of speciation: allopatric speciation followed by range expansion and subsequent stasis. Leiogalathea started diversifying during the Oligocene, likely in the Tethyan. The Atlantic lineage then split from its Indo-Pacific sister group due to vicariance driven by closure of the Tethys Seaway. The Atlantic lineage is less speciose compared with the Indo-Pacific lineages, with the Tropical Southwestern Pacific being the current centre of diversity. Leiogalathea diversification coincided with cladogenetic peaks in shallow-water genera, indicating that historical biogeographic events similarly shaped the diversification and distribution of both deep-sea and shallow-water squat lobsters.

A new genus and species in the caridean shrimp family Palaemonidae is described based on three type specimens collected at a depth range of 208-385 m off Guadeloupe, French Antilles. Zoukaris festivus gen. et sp. nov. shares many characters with several western Atlantic deep-water species currently assigned to Periclimenes Costa, 1844, as well as with the monotypic western Atlantic genus Diapontonia Bruce, 1986 and the Indo-West Pacific genus Echinopericlimenes Marin Chan, 2014. Zoukaris gen. nov. can be separated from all of them by a unique combination of morphological features, especially the configuration of the dactylus of the ambulatory pereiopods. In addition, Periclimenes milleri Bruce, 1986 is recorded from the French Antilles based on a single specimen, also from Guadeloupe; its colour pattern is illustrated for the first time.

There is a growing interest in the management of seamounts of the Southwestern Indian Ocean (SWIO) both in waters under national jurisdictions and in the Areas Beyond National Jurisdiction (ABNJ). New scientific knowledge has been gathered through various oceanographic cruises during the past decade, and new agreements are under consideration globally to promote conservation and sustainable use of the biodiversity in the ABNJ, where the deep sea ecosystems associated with seamounts are a growing matter of concern. SWIO seamounts have attracted the interests of fishers since the 1960s, and contracts for mining exploration have been granted recently. Seamounts are known to shelter rich, fragile and poorly resilient ecosystems whose important ecological functions are threatened by various anthropogenic pressures. Whereas many seamounts and shoals are located in national waters, many others fall in the ABNJ, with no current legal status per se. To ensure conservation of their habitats and biodiversity, it is essential that protection measures are instigated under an internationally recognized legal and institutional framework. In this paper, we review the current state of such a framework relevant to seamounts, with emphasis on fisheries and conservation in the SWIO. An emblematic seamount, the Walters Shoal, is selected as a case study to discuss how it could become a fully-protected space in the ABNJ. As a large part of the SWIO is under the mandate of the Nairobi Convention (as a Regional Sea under the auspices of UNEP), guidelines are proposed to encourage dedicated seamount governance within the framework of this Convention.

An examination of the deep-sea barnacles (Cirripedia, Thoracica) collected by the Karubar expedition to Indonesia (1991) and deposited in the Muséum National d’Histoire Naturelle, Paris, identified 40 species contained in three families of stalked and five families of acorn barnacles. Information on these species is presented, including descriptions, updated distributions and images to aid species identification. Thirty of the species, treated herein, are new records for the Indonesian Kei Islands and Tanimbar Island, which increases the total number of species recorded from Kei Islands, Aru Island and Tanimbar Island to 40. This study demonstrates the value of museum collections as a resource in biodiversity science.