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The performance of DNA metabarcoding approaches for characterizing biodiversity can be influenced by multiple factors. Here, we used morphological assessment of taxa in zooplankton samples to develop a large barcode database and to assess the congruence of taxonomic identification with metabarcoding under different conditions. We analysed taxonomic assignment of metabarcoded samples using two genetic markers (COI, 18S V1–2), two types of clustering into molecular operational taxonomic units (OTUs, ZOTUs), and three methods for taxonomic assignment (RDP Classifier, BLASTn to GenBank, BLASTn to a local barcode database). The local database includes 1042 COI and 1108 18S (SSU) barcode sequences, and we added new high-quality sequences to GenBank for both markers, including 109 contributions at the species level. The number of phyla detected and the number of taxa identified to phylum varied between a genetic marker and among the three methods used for taxonomic assignments. Blasting the metabarcodes to the local database generated multiple unique contributions to identify OTUs and ZOTUs. We argue that a multi-marker approach combined with taxonomic expertise to develop a curated, vouchered, local barcode database increases taxon detection with metabarcoding, and its potential as a tool for zooplankton biodiversity surveys.

A new genus of ectoparasitic marine annelids living on ctenophores, Ctenophoricola gen. nov., is described and its feeding behaviour, reproduction and developmental stages are discussed. Its unusual morphology challenged its placement within the known marine families. However, analyses of mitochondrial and nuclear sequence data showed the new genus as member of the Alciopini, a group of holopelagic annelids included within the Phyllodocidae. Ctenophoricola masanorii sp. nov. from Japan and Ctenophoricola rousei sp. nov. from the Canary Islands (Spain) are described. A third species from the Gulf of California is not formally described because the specimens are in poor condition. The new genus is characterized by having: 1) two distinctive body regions, the anterior with reduced parapodia lacking chaetae, and the posterior with long parapodia and chaetae and 2) a pair of large, elongate lensed eyes. These eyes are here described using histology and 3D reconstruction based on a Californian specimen. The two new species mainly differ in colour pattern, shape of parapodia, number of chaetae and body ciliation.

A new genus and species of Nerillidae, Nipponerilla irabuensis gen. nov., sp. nov., is described from an anchialine cave in Shimoji Island, west of Irabu Island (Miyako Islands, Southwestern Japan). Its morphology was examined with light, scanning electron, and confocal laser scanning microscopy. This new species, along with two putative new cave species from the Turks and Caicos Islands and several closely related nerillids, was included in a phylogenetic analysis employing five concatenated gene markers (16S rRNA, 18S rRNA, 28S rRNA, H3, and COI). Nipponerilla irabuensis gen. nov., sp. nov. was found to be sister taxon to the cave-exclusive genus Speleonerilla Worsaae, Sterrer & Iliffe, in Worsaae et al., 2019, but shows morphological resemblance to both Speleonerilla and Mesonerilla Remane, 1949. Thus, Nipponerilla gen. nov. constitutes a new monotypic genus in Nerillidae diagnosed by a combination of the following characters: nine segments, compound chaetae, high palp and antennae to body length ratios, and gonochoristic reproduction with two pairs of spermioducts opening in segments VII and VIII. Its placement among Nerillidae is discussed, along with its putative adaptations to an anchialine environment.

Remipedia is a stygobitic group commonly associated with coastal anchialine caves. This class consists of 12 genera, ten of which are found within the Lucayan Archipelago. Herein, we describe a new species within the genus Godzillius from Conch Sound Blue Hole, North Andros Island, Bahamas. Godzillius louriei sp. nov. is the third known remipede observed from a subseafloor marine cave, and the first from the Godzilliidae. Remipedes dwell within notoriously difficult to access cave habitats and thus integrative and comprehensive systematic studies at family or genus level are often absent in the literature. In this study, all species of Godzillius are compared using morphological and molecular approaches. Specifically, the feeding appendages of G. louriei sp. nov., G. fuchsi Gonzalez, Singpiel & Schlagner, 2013 and G. robustus Schram, Yager & Emerson, 1986 were examined using scanning electron microscopy (SEM). Species of Godzillius are identified based on the spines of maxilla 1 segment 4 and by the denticles on the lacinia mobilis of the left mandible. A molecular phylogeny using the mitochondrial 16S rRNA and nuclear histone 3 genes recovered G. louriei sp. nov. within the Godzillius clade and 16S genetic distances revealed a 13–15% difference between species of Godzillius.

Synopsis Aquatic animals have developed a wide array of adaptations specific to life underwater, many of which are related to moving in the water column. Different swimming methods have emerged, such as lift-based flapping, drag-based body undulations, and paddling. Patterns occur across scales and taxa, where animals with analogous body features use similar locomotory methods. Metachronal paddling is one such wide-spread propulsion mechanism, occurring in taxa as diverse as ctenophores, crustaceans, and polychaetes. Sequential movement of multiple, near identical appendages, allows for steady swimming through phase-offsets between adjacent propulsors. The soft-bodied, holopelagic polychaete Tomopteris has two rows of segmental appendages (parapodia) positioned on opposite sides along its flexible body that move in a metachronal pattern. The outer one-third of their elongate parapodia consist of two paddle-like pinnules that can be spread or, when contracted, fold together to change the effective width of the appendage. Along with metachronal paddling, tomopterid bodies undulate laterally, and by using high speed video and numerical modeling, we seek to understand how these two behaviors combine to generate effective swimming. We collected animals using deep-diving remotely operated vehicles, and recorded video data in shore- and ship-based imaging laboratories. Kinematics were analyzed using landmark tracking of features in the video data. We determined that parapodia are actively moved to generate thrust and pinnules are actively spread and contracted to create differences in drag between power and recovery strokes. At the same time, the body wave increases the parapodium stroke angle and extends the parapodia into undisturbed water adjacent to the body, enhancing thrust. Based on kinematics measurements used as input to a 1D numerical model of drag-based swimming, we found that spreading of the pinnules during the power stroke provides a significant contribution to propulsion, similar to the contribution provided by the body wave. We conclude that tomopterids combine two different propulsive modes, which are enabled by their flexible body plan. This makes their anatomy and kinematics of interest not only for biologists, but also for soft materials and robotics engineers.

Across Annelida, accessing the water column drives morphological and lifestyle modifications—yet in the primarily “benthic” scale worms, the ecological significance of swimming has largely been ignored. We investigated genetic, morphological and behavioural adaptations associated with swimming across Polynoidae, using mitogenomics and comparative methods. Mitochondrial genomes from cave and pelagic polynoids were highly similar, with non-significant rearrangements only present in cave Gesiella. Gene orders of the new mitogenomes were highly similar to shallow water species, suggestive of an underlying polynoid ground pattern. Being the first phylogenetic analyses to include the holopelagic Drieschia, we recovered this species nested among shallow water terminals, suggesting a shallow water ancestry. Based on these results, our phylogenetic reconstructions showed that swimming evolved independently three times in Polynoidae, involving convergent adaptations in morphology and motility patterns across the deep sea (Branchipolynoe), midwater (Drieschia) and anchialine caves (Pelagomacellicephala and Gesiella). Phylogenetic generalized least-squares (PGLS) analyses showed that holopelagic and anchialine cave species exhibit hypertrophy of the dorsal cirri, yet, these morphological modifications are achieved along different evolutionary pathways, i.e., elongation of the cirrophore versus style. Together, these findings suggest that a water column lifestyle elicits similar morphological adaptations, favouring bodies designed for drifting and sensing.

Gelatinous zooplankton are increasingly acknowledged to contribute significantly to the carbon cycle worldwide, yet many taxa within this diverse group remain poorly studied. Here, we investigate the pelagic tunicate Pyrosoma atlanticum in the waters surrounding the Cabo Verde Archipelago. By using a combination of pelagic and benthic in situ observations, sampling, and molecular genetic analyses (barcoding, eDNA), we reveal that: P. atlanticum abundance is most likely driven by local island-induced productivity, that it substantially contributes to the organic carbon export flux and is part of a diverse range of biological interactions. Downward migrating pyrosomes actively transported an estimated 13% of their fecal pellets below the mixed layer, equaling a carbon flux of 1.96–64.55 mg C m−2 day−1. We show that analysis of eDNA can detect pyrosome material beyond their migration range, suggesting that pyrosomes have ecological impacts below the upper water column. Moribund P. atlanticum colonies contributed an average of 15.09 ± 17.89 (s.d.) mg C m−2 to the carbon flux reaching the island benthic slopes. Our pelagic in situ observations further show that P. atlanticum formed an abundant substrate in the water column (reaching up to 0.28 m2 substrate area per m2), with animals using pyrosomes for settlement, as a shelter and/or a food source. In total, twelve taxa from four phyla were observed to interact with pyrosomes in the midwater and on the benthos.

Annelids are predominantly found along with the seafloor, but over time have colonized a vast diversity of habitats, such as the water column, where different modes of locomotion are necessary. Yet, little is known about their potential muscular adaptation to the continuous swimming behaviour required in the water column. The musculature and motility were examined for five scale worm species of Polynoidae (Aphroditiformia, Annelida) found in shallow waters, deep sea or caves and which exhibit crawling, occasional swimming or continuous swimming, respectively. Their parapodial musculature was reconstructed using microCT and computational three-dimensional analyses, and the muscular functions were interpreted from video recordings of their locomotion. Since most benthic scale worms are able to swim for short distances using body and parapodial muscle movements, suitable musculature for swimming is already present. Our results indicate that rather than rearrangements or addition of muscles, a shift to a pelagic lifestyle is mainly accompanied by structural loss of muscle bundles and density, as well as elongation of extrinsic dorsal and ventral parapodial muscles. Our study documents clear differences in locomotion and musculature among closely related annelids with different lifestyles as well as points to myoanatomical adaptations for accessing the water column.

Aegiochus gracilipes Hansen, 1895 was described from a single immature specimen accompanied by three figures (Hansen 1895). Hansen (1916) subsequently reported the species without figures. Over the next 100 years A. gracilipes only appeared in the literature as a citation in larger review and cataloguing studies. Most significantly, Bruce (2009) transferred A. gracilipes from Aega Leach, 1815 to Aegiochus Bovallius, 1885, as part of a broader study redefining the morphological characters used to distinguish Aegiochus. To the present day A. gracilipes, described from the north-eastern Atlantic off the Outer Hebrides, Scotland, is known only from the original figures and its limited primary description.

At oceanic depths200 m, there is little ambient sunlight, but bioluminescent organisms provide another light source that can reveal animals to visual predators and prey [1-4]. Transparency and mirrored surfaces-common camouflage strategies under the diffuse solar illumination of shallower waters-are conspicuous when illuminated by directed bioluminescent sources due to reflection from the body surface [5, 6]. Pigmentation allows animals to absorb light from bioluminescent sources, rendering them visually undetectable against the dark background of the deep sea [5]. We present evidence suggesting pressure to reduce reflected bioluminescence led to the evolution of ultra-black skin (reflectance0.5%) in 16 species of deep-sea fishes across seven distantly related orders. Histological data suggest this low reflectance is mediated by a continuous layer of densely packed melanosomes in the exterior-most layer of the dermis [7, 8] and that this layer lacks the unpigmented gaps between pigment cells found in other darkly colored fishes [9-13]. Using finite-difference, time-domain modeling and comparisons with melanosomes found in other ectothermic vertebrates [11, 13-21], we find the melanosomes making up the layer in these ultra-black species are optimized in size and shape to minimize reflectance. Low reflectance results from melanosomes scattering light within the layer, increasing the optical path length and therefore light absorption by the melanin. By reducing reflectance, ultra-black fish can reduce the sighting distance of visual predators more than 6-fold compared to fish with 2% reflectance. This biological example of efficient light absorption via a simple architecture of strongly absorbing and highly scattering particles may inspire new ultra-black materials.

Eurycope producta Sars, 1868 and Eurycope inermis Hansen, 1916 are two widely distributed and highly abundant isopod species complexes within Icelandic waters, a region known for its highly variable environment. The two species complexes have bathymetric depth ranges from 103 to 2029 m (E. producta) and from 302 to 2113 m (E. inermis). Molecular evidence was used for species delimitation within these species complexes by analyzing nuclear (18S rDNA, H3) and mitochondrial (16S rDNA, COI) sequence data. Tree-based methods (BI and ML) and four species delimitation methods (ABGD, GMYC, NDT, PTP) were applied, in order to disentangle the two species complexes. A total of eight and four species clades could be identified within samples of the E. producta and E. inermis complexes and respectively included the closely related species E. dahli Svavarsson, 1987; E. hanseni Ohlin, 1901; and E. cornuta Sars, 1864. The morphological findings coincide with the observed molecular species clades. The elucidated species clades were geographically and bathymetrically much more restricted than previously assumed. Eight species clades featured depth spans of less than 400 m and only four species clades featured depth spans of 1000 to 1500 m. Only two species clades (E. producta sensu stricto and E. inermis sensu stricto) were found on both sides of the Greenland-Scotland Ridge. Further, species distribution maps were generated using random forest, to predict potential distributional patterns for the resolved species clades of the two species complexes. We present the first attempt of combining morphological, molecular, and species distribution models in marine isopods thus far.

Highlights: • The holopelagic amphipod Paraphronima is shown to contain hidden genetic diversity. • Diversity appears biogeographically restricted to regional scales. • A new species is described using a morpho-molecular approach. • Compound eye characters are shown to be useful in distinguishing species. • The inclusion of compound eyes is recommended in taxonomic studies of Hyperiidea. Holopelagic animals were long assumed to have widespread geographic distributions due to the failure to recognize hydrographic species' barriers in the open ocean. As molecular genetic tools are more commonly used to study the ocean's inhabitants, diversity is found to be substantially higher than when inferred from morphological taxonomies alone. Here, we investigate the morphological and genetic diversity of hyperiid amphipods within the genus Paraphronima, currently comprising two supposedly cosmopolitan species. By combining phylogenetic analyses and four species delimitation methods (GMYC, mPTP, bPTP, ABGD), we reveal substantial species-level genetic variation. Instead of two species inhabiting multiple ocean basins, the biogeography of Paraphronima species appears to be limited to more regional scales. Moreover, there is morphological evidence to corroborate the observed genetic diversity. By using an integrative morpho-molecular approach, a third species from the Gulf of California, Paraphronima robisoni sp. nov., is described. Interestingly, the morphological characters that best distinguish the species within the genus are characters of the compound eyes, which have rarely been used for taxonomy despite being the most obvious and varied features of hyperiids. Our results warrant further investigation of presumably cosmopolitan holopelagic amphipods, while we recommend the inclusion of eye morphology in future taxonomic studies.

Lying at the southernmost point of the Lucayan Archipelago, the Turks and Caicos Islands are amongst the better studied localities for anchialine cave biodiversity. For nearly five decades, novel invertebrate fauna, comprised primarily of crustaceans, have been collected from these tidally influenced pools – but new findings are always on the horizon. Herein we present new records of crustaceans and annelids from anchialine blue holes and horizontal caves of the Turks and Caicos. These findings include two potentially new species of meiofaunal annelids and a new species of remipede collected from a shallow water cave pool. Our 2019 expedition additionally expands known faunal distributions for several taxa across the Caicos islands, and raises the biodiversity of the region to 35 species, 13 of them considered endemic. This is the first comprehensive faunal list for the anchialine systems in the Caicos Bank.

Summary Transparent zooplankton and nekton are often nearly invisible when viewed under ambient light in the pelagic zone [1–3]. However, in this environment, where the light field is directional (and thus likely to cause reflections), and under the bioluminescent searchlights of potential predators, animals may be revealed by reflections from their body surface [4–7]. We investigated the cuticle surfaces of seven species of hyperiids (Crustacea; Amphipoda) using scanning electron microscopy and found two undocumented features that may reduce reflectance. We found that the legs of Cystisoma spp. (n = 5) are covered with an ordered array of nanoprotuberances 200 ± 20 nm SD in height that function optically as a gradient refractive index material [6, 8, 9]. Additionally, we observed that Cystisoma and six other species of hyperiids are covered with a monolayer of homogenous spheres (diameters ranging from 52 ± 7 nm SD on Cystisoma spp. to 320 ± 15 nm SD on Phronima spp.). Optical modeling using effective medium theory and transfer matrix methods demonstrated that both the nanoprotuberances and the monolayers reduce reflectance by as much as 100-fold, depending on the wavelength and angle of the incident light and the thickness of the gradient layer. Even though we only consider surface reflectance and not internal light scattering, our study demonstrates that these nanoprotuberances and spheres can improve crypsis in a featureless habitat where the smallest reflection can render an animal vulnerable to visual predation.

4/2/2019 – 24/2/2019, Mindelo (Republic of Cape Verde) – Mindelo (Republic of Cape Verde) DeepC-Jelly We proposed to test the hypothesis that large gelatinous macrozooplankton (e.g. tunicates, hydrozoans) are a significant carbon storage in midwater, and a vector for carbon from midwater to the ocean floor in Cape Verde. To test this hypothesis, we studied 1) the distribution, diversity and abundance of gelatinous organisms in the epi-, meso-, and bathypelagic zone, 2) their role in transporting carbon through the pelagic foodweb to the seafloor and 3) their behavior and associations. We worked in the coastal deep sea off Santo Antao and Fogo as well as in the open ocean at the time series station CVOO and an eddy. A manned submersible was used for mesopelagic surveys, to document the behaviour and associations of deep-sea organisms and to collect living specimens. We performed pelagic video transects, discrete net sampling, and eDNA sampling down to 3000 m. ADCP and CTD transects allowed a detailed reconstruction of the effect of the islands on currents and productivity. To quantify the carbon flux of pelagic foodfalls, we also surveyed the seafloor. Sample and video analysis is still in progress, but first results indicate the impact of the pelagic tunicate Pyrosoma atlanticum, which is an upwelling-favored species largely absent from the oligotrophic open ocean, in the nearshore regions of Cape Verde as well as in the cyclonic eddy sampled. It was also observed on the seafloor and resembles a food source and a habitat in the water column and in the benthos. Specimens of pelagic fauna were collected that allow new species descriptions. New records and a new species for the region were also observed during benthic surveys. The cruise was documented in various outreach activities including national television in Cabo Verde.

Summary The mesopelagic habitat is a vast space that lacks physical landmarks and is structured by depth, light penetration, and horizontal currents. Solar illumination is visible in the upper 1,000 m of the ocean, becoming dimmer and spectrally filtered with depth—generating a nearly monochromatic blue light field [1]. The struggle to perceive dim downwelling light and bioluminescent sources and the need to remain unseen generate contrasting selective pressures on the eyes of mesopelagic inhabitants [2]. Hyperiid amphipods are cosmopolitan members of the mesopelagic fauna with at least ten different eye configurations across the family—ranging from absent eyes in deep-living species to four enlarged eyes in mesopelagic individuals [3–7]. The hyperiid amphipod Paraphronima gracilis has a pair of bi-lobed apposition compound eyes, each with a large upward-looking portion and a small lateral-looking portion. The most unusual feature of the P. gracilis eye is that its upward-looking portion is resolved into a discontinuous retina with 12 distinct groups, each serving one transverse row of continuously spaced facets. On the basis of eye morphology, we estimated spatial acuity (2.5° ± 0.11°, SEM; n = 25) and optical sensitivity (30 ± 3.4 μm 2 ⋅ sr, SEM; n = 25). Microspectrophotometry showed that spectral sensitivity of the eye peaked at 516 nm (±3.9 nm, SEM; n = 6), significantly offset from the peak of downwelling irradiance in the mesopelagic realm (480 nm). Modeling of spatial summation within the linear retinal groups showed that it boosts sensitivity with less cost to spatial acuity than more typical configurations.

Loss or stark reduction of the free-swimming medusa or jellyfish stage is common in the cnidarian class Hydrozoa. In the hydrozoan clade Trachylina, however, many species do not possess a sessile polyp or hydroid stage. Trachylines inhabiting freshwater and coastal ecosystems (i.e., Limnomedusae) possess a metagenetic life cycle involving benthic, sessile polyp and free-swimming medusa. In contrast, the paradigm is that open ocean inhabiting, oceanic trachylines (in the orders Narcomedusae and Trachymedusae) develop from zygote to medusa via a free-swimming larva, forgoing the polyp stage. In some open-ocean trachylines, development includes a sessile stage that is an ecto- or endoparasite of other oceanic organisms. We expand the molecular-based phylogenetic hypothesis of trachylines significantly, increasing taxon and molecular marker sampling. Using this comprehensive phylogenetic hypothesis in conjunction with character state reconstructions we enhance understanding of the evolution of life cycles in trachyline hydrozoans. We find that the polyp stage was lost at least twice independently, concurrent with a transition to an oceanic life style. Further, a sessile, polypoid parasitic stage arose once, rather than twice as current classification would imply, in the open ocean inhabiting Narcomedusae. Our results also support the hypothesis that interstitial species of the order Actinulida are directly descended from direct developing, oceanic trachylines.

Pteropods are a widespread group of holoplanktonic gastropod molluscs and are uniquely suitable for study of long-term evolutionary processes in the open ocean because they are the only living metazoan plankton with a good fossil record. Pteropods have been proposed as bioindicators to monitor the impacts of ocean acidification and in consequence have attracted considerable research interest, however, a robust evolutionary framework for the group is still lacking. Here we reconstruct their phylogenetic relationships and examine the evolutionary history of pteropods based on combined analyses of Cytochrome Oxidase I, 28S, and 18S ribosomal rRNA sequences and a molecular clock calibrated using fossils and the estimated timing of the formation of the Isthmus of Panama. Euthecosomes with uncoiled shells were monophyletic with Creseis as the earliest diverging lineage, estimated at 41–38 million years ago (mya). The coiled euthecosomes (Limacina, Heliconoides, Thielea) were not monophyletic contrary to the accepted morphology-based taxonomy; however, due to their high rate heterogeneity no firm conclusions can be drawn. We found strong support for monophyly of most euthecosome genera, but Clio appeared as a polyphyletic group, and Diacavolinia grouped within Cavolinia, making the latter genus paraphyletic. The highest evolutionary rates were observed in Heliconoides inflatus and Limacina bulimoides for both 28S and 18S partitions. Using a fossil-calibrated phylogeny that sets the first occurrence of coiled euthecosomes at 79–66 mya, we estimate that uncoiled euthecosomes evolved 51–42 mya and that most extant uncoiled genera originated 40–15 mya. These findings are congruent with a molecular clock analysis using the Isthmus of Panama formation as an independent calibration. Although not all phylogenetic relationships could be resolved based on three molecular markers, this study provides a useful resource to study pteropod diversity and provides general insight into the processes that generate and maintain their diversity in the open ocean.

A 2009 oceanographic expedition of the Russian Academy of Sciences collected the anterior region of a single acorn worm (phylum Hemichordata, class Enteropneusta) by trawling at a depth of 5560 m in the Romanche Trench (equatorial Atlantic). The specimen was a ripe female with numerous, relatively small oocytes in each ovary. Phylogenetic analysis of rDNA sequences robustly placed the worm in the family Spengelidae. In addition, morphological features of the proboscis, collar, and anterior trunk region indicated that the worm wasGlandiceps abyssicola, a species previously represented solely by the holotype, which had been dredged from the equatorial Atlantic in 1873 by the HMS ‘Challenger’ and subsequently sent to Germany for description by Spengel (1893). The holotype was presumably destroyed by World War II bombing; therefore, we here designate the Romanche Trench specimen as the neotype ofG. abyssicolaand supply an augmented species diagnosis.

Sphaerodoridae (Annelida) is a seeming uncommon and minimally diverse group of polychaetes in the northwestern Atlantic, with only seven species reported from the United States, and none from the eastern coast of Canada, before the present study. Review of the large Smithsonian collection (National Museum of Natural History, Washington) revealed the presence of two morphologically extraordinary undescribed species and added a new record to the north-western Atlantic region. Euritmia carolensis sp. n. is characterised by bearing approximately 20 sessile spherical papillae arranged in three transverse rows per segment, ventrum with 4–6 larger papillae near the parapodial bases and parapodia without papillae; bearing 4–5 simple chaetae that are enlarged subdistally. Sphaerephesia amphorata sp. n. is distinguished from other congeners in the presence of four longitudinal rows of sessile, bottle-shaped macrotubercles with exceptionally long digitiform terminal papilla, and parapodia with four rounded and small papillae, bearing 4–7 compound chaetae, with blades 7–11 times as long as wide. Other encountered species are also herein re-described, including intraspecific variation and updated iconography. Comparison of material also allowed some systematic changes in the group, including the synonymisation of the genus Amacrodorum with Euritmia, and the transfer of Ephesiopsis shivae to Ephesiella. A key to the species reported from the Northwestern Atlantic is provided., SEMs were taken in Museo Nacional de Ciencias Naturales de Madrid during a European Commission Taxonomic Initiative SYNTHESYS (ESTAF-2839)

Ninety-two individuals of a deep-sea harrimaniid enteropneust were imaged between 1675 m and 3225 m off the California coast. Of these, about three-fourths were positioned with their posterior regions buried in sediment or hidden by rocks, and the rest were completely exposed on the substratum. When visible, the posterior end of each worm was typically associated with a dense tangle of fecal strands. One specimen was captured and is described here as the holotype of Saxipendium implicatum. In life, it was 22 cm long, and the color of its dome-shaped proboscis, narrow collar, and anterior trunk was medium orange. No wing-like folds of the body wall protruded anywhere along the length of the worm. The proboscis complex included a stomochord and glomeruli, but neither a heart nor a pericardial cavity could be detected. Most of the dorsal collar nerve runs along an open invagination in the dorsal midline of the collar and is only roofed over very briefly at the posterior extremity of the collar. Anot...

Enteropneusts in the family Torquaratoridae were imaged using still and video cameras in the deep North Atlantic and then collected by remotely operated vehicles. From this material, we describe Yoda purpurata n. gen, n. sp., Tergivelum cinnabarinum n. sp., and Allapasus isidis n. sp. Individuals of the first two species were browsing completely exposed on the sea floor, whereas the specimen of the last species was encountered floating ~1 m above the sea floor. Living specimens of Y. purpurata were 12–19 cm long and had a dark reddish-purple proboscis, collar, and genital wings (folded dorsally over the anterior region of the trunk). Members of this species were hermaphrodites (the first ever discovered in the phylum Hemichordata), with numerous separate testes and ovaries in the genital wings. Living specimens of T. cinnabarinum were 12–26 cm long and had a cinnabar-colored proboscis, collar, and back veils (arising from the anterior region of the trunk); sexes were separate, and body shape and internal morphology closely resemble those of its brown congener, T. baldwinae, from the eastern Pacific. The only specimen of A. isidis collected was a male 13 cm long and pale yellow when alive. Its body shape was proportionally shorter and broader than that of its orange congener, A. aurantiacus, from the eastern Pacific, but the internal anatomy of the two species is virtually identical. [Correction made after online publication August 21, 2012 to correct species name in preceding sentence.]

Two new species of Swima, a recently established genus of annelid worms, are introduced, one from deep water off the North American West Coast and the other from the Philippines. The acrocirrid genus now contains three named species, Swima bombiviridis, Swima fulgida sp. nov., and Swima tawitawiensis sp. nov.Swima are holopelagic, occurring only in the water column, and thus far have only been observed below 2700 m. The worms are relatively large, sometimes reaching over 30 mm in length and 5 mm in width. They have gelatinous bodies and fans of long swimming chaetae, which are flattened into paddles in S. tawitawiensis sp. nov. Members of Swima are distinguished from other swimming acrocirrids by their transparent bodies, single medial subulate branchiae, and simple nuchal organs that do not skirt the bases of lateral subulate branchiae. Swima fulgida sp. nov. is distinguished from other members of the genus by its darkly pigmented anterior gut, whereas S. tawitawiensis sp. nov. is distinguished by possessing three subulate head appendages instead of just one and by the shape of its noto- and neurochaetae. Swima species possess four pairs of elliptical, transformed segmental branchiae that produce green bioluminescence when autotomized. These ‘bombs’ were observed in various states of regeneration on a single individual. Swima are neutrally buoyant, often observed hanging immobile in the water column, and are active, agile swimmers. Although not previously documented in the literature, these worms are not rare in the deep water column. Since the worms were first noticed in 2001, they have been observed on more than half of the Monterey Bay Aquarium Research Institute's midwater remotely operated vehicle dives that went to sufficient depth. The discovery of Swima underscores our lack of knowledge of deep pelagic fauna. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 163, 663–678.

Recent warming in the Antarctic has led to increased production of icebergs; however, the ecological effects of icebergs on pelagic communities within the Southern Ocean have not been well-studied. We used a 10 m 2 MOCNESS to collect macrozooplankton and micronekton in the upper 300 m of the water column near free-drifting icebergs in the Atlantic sector of the Southern Ocean during three seasons: December 2005 (late spring), June 2008 (late fall) and March-April 2009 (late summer). Communities were dominated in all three seasons by Antarctic krill ( Euphausia superba ) and salps ( Salpa thompsoni ), which collectively comprised 60-95% of the community wet biomass in most cases. During our spring and summer cruises, mean biomass was elevated by 3.1-4.3x at a distance of 0.37 km from large icebergs vs . 9.26 km away. These differences were not statistically significant, and no trend in biomass with distance was apparent in samples from fall 2008, when total biomass was an order of magnitude lower. Biomass levels near icebergs during Dec 2005 and Mar-Apr 2009 were comparable to values reported from marginal ice zones, suggesting that waters around icebergs support macrozooplankton and micronekton communities comparable in magnitude to those in some of the most productive areas of the Southern Ocean. Sample variance also was significantly higher within 1.85 km of icebergs during Dec 2005 and Mar-Apr 2009, reflecting increased patchiness on scales sampled by the MOCNESS (20–40×10 3 m 3 filtered per sample). This pattern was not significant during Jun 2008. Large predatory medusae were observed within 1.85 km of icebergs and in Iceberg Alley, an area through which icebergs pass frequently, but were virtually absent in areas remote from icebergs. Small euphausiids showed an inverse distribution, with low densities in areas populated by large medusae. A shift in community composition from a near-iceberg assemblage dominated by herbivores to a carnivore-dominated community in Iceberg Alley may reflect a transition from bottom-up to top-down control with increasing distance and time. Body sizes of dominant species varied seasonally but did not show consistent trends with distance from icebergs. Concentrations of photosynthetic pigments in the guts of E. superba and S. thompsoni corresponded broadly to patterns in surface chlorophyll a concentrations and were comparable to maximum gut pigment concentrations measured in animals collected from highly productive marginal ice zones. Our results suggest that the macrozooplankton and micronekton assemblages near free-drifting icebergs can be quantitatively and qualitatively different from those in surrounding, iceberg-free waters, perhaps due to both bottom-up and top-down processes as well as physical forcing by the passage of a large object through the upper ocean.

We investigated the habitat depth and population dynamics of mesopelagic foraminifera in Monterey Bay, California, using 12 yr of video surveys and specimens from live collections. The water column over Monterey Canyon continuously supports two distinct species of mesopelagic foraminifera, Hastigerinella digitata and a previously unknown species referred to as Hastigerina sp., with H. digitata dominating the planktonic foraminiferal assemblage at mesopelagic depths. H. digitata populations live within a narrow depth horizon that lies above the core of the regional oxygen minimum zone at a depth of 280–358 m and O2 concentrations of 1–1.3 mL L−1. Our observations provide a modern calibration for understanding fossil digitate planktonic foraminifera. We observed numerous copepods in various stages of ingestion on the spines of H. digitata and a conspicuous lack of detritus attached to the spine network, providing support for the hypothesis that H. digitata is an obligate carnivore. H. digitata populations did not show the strong two-phase seasonality that characterizes the population dynamics of many mesopelagic species that live above the Monterey Canyon, although H. digitata was generally more abundant in cooler waters on seasonal and interannual timescales.

Osborn, K. J. & Rouse, G. W. (2010). Phylogenetics of Acrocirridae and Flabelligeridae (Cirratuliformia, Annelida). —Zoologica Scripta, 40, 204–219. When seven deep-sea, swimming cirratuliforms were recently discovered, the need for a thorough phylogenetic hypothesis for Cirratuliformia was clear. Here, we provide a robust phylogenetic hypothesis for the relationships within Acrocirridae and increase the taxon sampling and resolution within Flabelligeridae based on both molecular (18S, 28S, 16S, COI and CytB) and morphological data. Data partitions were analyzed separately and in combination. Acrocirridae and Flabelligeridae were reciprocally monophyletic sister groups when rooted by cirratulids. The seven recently discovered species form a clade within Acrocirridae and will be designated as four genera based on phylogenetic relationships and apomorphies. A revised diagnosis is provided for Swima, restricting the genus to three species distinguished by a thick gelatinous sheath, transparent body, simple nuchal organs, a single medial subulate branchia, and four pair of small segmental branchiae modified as elliptical, bioluminescent sacs. Helmetophorus and Chauvinelia are maintained as separate genera based on morphological differences. Evidence for flabelligerid branchiae being segmental is provided, the papillae on segment two of most acrocirrids is confirmed to be the nephridiopores, and scanning electron microscopy is used to examine acrocirrid spinous chaetae in comparison with flabelligerid segmented chaetae.

The Munnopsidae are a diverse group of asellote isopods that are an important component of deep-sea fauna. Morphologically-based phylogenetic inference attempts have proven to be of limited use due to the ecological and morphological diversity within the clade. Monophyly of the family is well-established but relationships within the group remain unresolved. This project is the first molecularly-based effort focused specifically on resolving phylogenetic relationships within the Munnopsidae. Partial 28S and COI and complete 18S genes were sequenced for 28 asellotes, 15 additional taxa were included from which only one or two of the three target sequences could be obtained, and 18S sequences for five additional taxa were available from GenBank. Sequences were analysed both as individual genes and in combination using Bayesian and maximum parsimony approaches. Each gene provided a phylogenetic signal that could be identified in the combined analyses, with 18S analyses providing the most resolution of phylogenetic relationships. The available representatives of subfamilies Munnopsinae and Ilyarachninae were monophyletic, as was the genus Munneurycope. Relationships within the subfamily Munnopsinae were well-resolved by thorough taxon sampling, several new species were placed, and the need for taxonomic revision of Munnopsis/Munnopsoides was supported. These analyses supported putative Eurycope paraphyly and emphasized the need for careful revision of this highly variable genus. Tytthocope was sister to Munnopsurus. Syneurycope was suggested as the sister group to the ilyarachnines. Combined analyses provided increased support for clades suggested in at least two individual gene analyses and for clades not strongly contradicted by individual analyses. Further work is required to fully resolve the munnopsid phylogeny and should consist of increased taxon sampling for the complete 18S sequence and possibly identification of at least one slowly evolving, nuclear protein-coding gene to resolve the basal polytomy and enable placement of the root.

An extraordinary new species, Chaetopterus pugaporcinus, is described from eight specimens collected from deep mesopelagic waters off Monterey Bay, California, by remotely operated vehicles. All specimens exhibit a consistent combination of both adult and larval characteristics, leaving in question the maturity of the specimens. All specimens lack ciliated larval bands and the stout, modified chaetae (cutting spines) typically found in segment A4 of chaetopterids. If the specimens described here are larvae, they are remarkable for their size, which ranged from 10 to 21 mm total length, nearly twice the length of the largest polychaete larvae previously reported and 5 to 10 times larger than known chaetopterid larvae. Then too, their lack of segment addition prior to settlement would be atypical. If adult, they are particularly unusual in their habitat choice and body form. Morphology of the uncini and comparison to larval morphology indicated a close relationship to either Chaetopterus or Mesochaetopterus. However, the lack of cutting spines and typical adult morphology made it impossible to determine to what genus this species should be allied. Thus, we carried out the first molecular phylogenetic analysis of the Chaetopteridae in order to appropriately place and name the new species. Three partial genes were sequenced for 21 annelid species. The sequencing also provides the first molecular evidence that Chaetopterus variopedatus sensu Hartman (1959) is not a single cosmopolitan species. The question of C. pugaporcinus being a delayed larva or a genuine holopelagic chaetopterid is discussed.

Tetraplatia is a genus containing two species of pelagic cnidarians of curious morphology. Their vermiform shape and four swimming flaps are difficult to relate to the features of other cnidarians, thus obscuring their phylogenetic affinities. Since their discovery in the mid-1800s, a number of prominent cnidarian workers have weighed in on this conundrum, some arguing that they are aberrant hydrozoans and others concluding that they are unusual scyphozoans. Current taxonomic practice conforms to the latter view. However, data presented here from the large and small subunits of the nuclear ribosome leave little doubt that Tetraplatia is in fact a hydrozoan genus. Indeed, its precise phylogenetic position is within Narcomedusae, as some authors had previously deduced based on structural characters. The distinctive body plan of Tetraplatia is remarkable because it appears to have a recent origin, in contrast to the prevailing pattern of metazoan history.

A single specimen of a previously undescribed acorn worm in the family Torquaratoridae was trawled from a bottom depth of about 350 m in the Kara Sea (Russian Arctic). The new species is the shallowest of the exclusively deep-sea torquaratorids found to date, possibly an example of high-latitude emergence. On the basis of ribosomal DNA sequences and morphology, the worm is described here as the holotype of Coleodesmium karaensis n. gen., n. sp. It is most similar in overall body shape to the previously described enteropneust genus Allapasus, but is uniquely characterized by a tubular component of the proboscis skeleton ensheathing the collar nerve cord. Additionally, within the proboscis, the sparseness of the musculature of C. karaensis clearly distinguishes it from the much more muscular members of Allapasus. The holotype is a female bearing about a dozen embryos on the surface of her pharyngeal region, each recessed within a shallow depression in the dorsal epidermis. The embryos, ranging from late gastrula to an early stage of coelom formation, are a little more than 1 mm in diameter and surrounded by a thin membrane. Each embryo comprises an external ectoderm of monociliated cells (not arranged in obvious ciliated bands) and an internal endo-mesoderm; the blastopore is closed. In the most advanced embryos, the anterior coelom is starting to constrict off from the archenteron. Coleodesmium karaensis is the first enteropneust (and indeed the first hemichordate) found brooding embryos on the surface of the mother's body.

Eulepethidae is a family of scale-bearing polychaetes. Although members of this family are common inhabitants of tropical and subtropical coastal waters, their diversity is low, with only 22 recognized species in six genera. Here we describe Eulepethus nanhaiensis sp. nov. based on 12 specimens collected from the coastal waters of the northern South China Sea. This new species can be distinguished from Eulepethus hamifer, the only previously described species in this genus, by having up to two spade-shaped lateral processes in some of the anterior elytrae, a blunt-tipped acicular chaeta in the neuropodia of segment 3, and a pair of non-overlapping elytrae in each posterior segment. Phylogenetic analysis indicates that Grubeulepis and Mexieulepis are sister genera, and these two genera form the sister clade of Eulepethus.

Enteropneusts (phylum Hemichordata), although studied extensively because of their close relationship to chordates, have long been considered shallow-water, burrowing animals. The present paper more than doubles the number of enteropneust species recorded in the deep sea based on high-resolution imaging and sampling with remotely operated vehicles. We provide direct evidence that some enteropneusts are highly mobile—using changes in posture and currents to drift between feeding sites—and are prominent members of deep, epibenthic communities. In addition, we provide ecological information for each species. We also show that despite their great morphological diversity, most deep-living enteropneusts form a single clade (the rediagnosed family Torquaratoridae) on the basis of rDNA sequences and morphology of the proboscis skeleton and stomochord. The phylogenetic position of the torquaratorids indicates that the group, after evolving from near-shore ancestors, radiated extensively in the deep sea.

An intriguing new annelid, Teuthidodrilus samae (Annelida, Cirratuliformia) gen. and sp. nov., was observed and collected during deep-water column exploration of the western Celebes Sea. The Celebes Sea is a deep pocket basin, effectively isolated from surrounding deep water, and is part of the Coral Triangle, a focal area for conservation because of its high diversity and unique geological history. Collected specimens reached 94 mm in length and possessed 10 anterior appendages that were as long or longer than the body. Two characters distinguish T. samae from other polychaetes: notochaetae forming broad, concavo-convex paddles and six pairs of free-standing, oppositely branched nuchal organs. Phylogenetic analysis of five genes and a 29-character morphological matrix showed that T. samae is an acrocirrid (primarily benthic polychaetes) belonging to the morphologically diverse swimming clade. Pelagic animals within primarily benthic clades are of particular interest in evolutionary biology, because their adaptations to life in the water column inform us of the evolutionary possibilities and constraints within the clade and indirectly of the selective pressures at work in this unfamiliar habitat. This new genus illustrates how much we have to learn about even the large, abundant inhabitants of deep-pelagic communities.

By using remotely operated vehicles, we found seven previously unknown species of swimming annelid worms below 1800 meters. Specimens were large and bore a variety of elaborate head appendages. In addition, five species have pairs of ellipsoidal organs homologous to branchiae that produce brilliant green bioluminescence when autotomized. Five genes were used to determine the evolutionary relationships of these worms within Cirratuliformia. These species form a clade within Acrocirridae and were not closely related to either of the two known pelagic cirratuliforms. Thus, this clade represents a third invasion of the pelagic realm from Cirratuliformia. This finding emphasizes the wealth of discoveries to be made in pelagic and deep demersal habitats.