Hadal Biodiversity, Habitats and Potential Chemosynthesis in the Java Trench, Eastern Indian Ocean

The Java Trench is the only subduction trench in the Indian Ocean that extends to the hadal zone (> 6,000 m water depth), and except for sevenbenthic trawls acquired around the 1950s, there has been little to no sampling at hadal depths undertaken since. In 2019, we undertook a 5-day expedition comprising a scientific dive using a full ocean depth-rated submersible, the DSV Limiting Factor, seven hadal-lander deployments, and high-resolution bathymetric survey. The submersible performed a video transect from the deepest point of the trench, up a 150 m high near-vertical escarpment located on the forearc, and then across a plateau at a depth of ∼7,050 m to make in situ observations of the habitat heterogeneity and biodiversity inhabiting these hadal depths. We found the Java Trench hadal community to be diverse and represented by 10 phyla, 21 classes, 34 orders and 55 families, with many new records and extensions in either depth or geographic range, including a rare encounter of a hadal ascidian. The submersible transect revealed six habitats spanning the terrain. The deepest trench axis comprised fine-grained sediments dominated by holothurians, whereas evidence of active rock slope failure and associated talus deposits were prevalent in near-vertical and vertical sections of the escarpment. Sediment pockets and sediment pouring down the steep wall in “chutes” were commonly observed. The slope terrain was dominated by two species in the order Actiniaria and an asteroid, as well as 36 instances of orange, yellow, and white bacterial mats, likely exploiting discontinuities in the exposed bedrock, that may indicate a prevalence of chemosynthetic input into this hadal ecosystem. Near the top of the escarpment was an overhang populated by > 100 hexactinellid (glass) sponges. The substrate of the plateau returned to fine-grained sediment, but with a decreased density and diversity of epifauna relative to the trench floor. By providing the first visual insights of the hadal habitats and fauna of the Java Trench, this study highlights how the habitat heterogeneity influences patchy species distributions, and the great benefit of using a hadal-rated exploratory vehicle to comprehensively assess the biodiversity of hadal ecosystems

Biogeography and phylogeny of the scavenging amphipod genus Valettietta (Amphipoda: Alicelloidea), with descriptions of two new species from the abyssal Pacific Ocean

Valettietta Lincoln & Thurston, 1983 (Amphipoda: Alicelloidea) is an infrequently sampled genus of scavenging amphipod, with a known bathymetric range from 17–5467 m encompassing a variety of habitats from anchialine caves to abyssal plains. Molecular systematics studies have uncovered cryptic speciation in specimens collected from the abyssal Pacific, highlighting uncertainty in the description of Valettietta anacantha (Birstein & Vinogradov, 1963). Here, we apply an integrative taxonomic approach and describe two new species, Valettietta trottarum sp. nov. and Valettietta synchlys sp. nov., collected at abyssal depths in the Clarion-Clipperton Zone, Pacific Ocean. Both species can be distinguished by characters of the gnathopods, uropod 3, and the inner plate of the maxilliped. Further, molecular phylogenetic analyses of two mitochondrial (16S rDNA and COI) and two nuclear (Histone 3 and 28S rRNA) regions found both new species to form well-supported clades and allowed us to re-identify previously published records based on genetic species delimitation. The biogeography of Valettietta is discussed in light of these re-evaluated records, and a new taxonomic key to the genus is provided. These new taxa highlight the strength of applying an integrated taxonomic approach to uncover biodiversity, which is critical in regions being explored for potential industrial purposes

Ship-to-shore training for active deep-sea capacity development

Sailing on scientific expeditions as an early career researcher (ECR) offers the beneficial opportunity to gain field experience and training. However, the number of available berths to achieve the scientific goals of an expedition limits the number of onboard participants. Telepresence and remote learning can be utilized to increase the number of active participants, broadening the reach of capacity development. The 2021 iMirabilis2 expedition on board the Spanish Research Vessel Sarmiento de Gamboa used telepresence to virtually involve ECRs from several countries in deep-sea science. One year post-expedition, a survey of onshore participants was conducted to assess and quantify the effectiveness of the peer-to-peer ECR ship-to-shore scheme. During the expedition, live, interactive training via WhatsApp and Zoom was utilized by onshore ECRs more than traditional static, unidirectional methods of blog posts and pre-recorded videos. All respondents either agreed or strongly agreed that the scheme provided an inclusive and accessible platform to share deep-sea science. These results suggest similar schemes could be used to supplement shorter-duration at-sea-training, used prior to a seagoing experience to better prepare ECRs, or to allow members of the science community unable to join an expedition in person to actively participate remotely, increasing inclusivity

Trajectories of Big Five Personality Traits: A Coordinated Analysis of 16 Longitudinal Samples

This study assessed change in self‐reported Big Five personality traits. We conducted a coordinated integrative data analysis using data from 16 longitudinal samples, comprising a total sample of over 60 000 participants. We coordinated models across multiple datasets and fit identical multi‐level growth models to assess and compare the extent of trait change over time. Quadratic change was assessed in a subset of samples with four or more measurement occasions. Across studies, the linear trajectory models revealed declines in conscientiousness, extraversion, and openness. Non‐linear models suggested late‐life increases in neuroticism. Meta‐analytic summaries indicated that the fixed effects of personality change are somewhat heterogeneous and that the variability in trait change is partially explained by sample age, country of origin, and personality measurement method. We also found mixed evidence for predictors of change, specifically for sex and baseline age. This study demonstrates the importance of coordinated conceptual replications for accelerating the accumulation of robust and reliable findings in the lifespan developmental psychological sciences. © 2020 European Association of Personality PsychologyPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/156004/1/per2259.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/156004/2/per2259-sup-0001-Data_S1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/156004/3/per2259-sup-0002-Open_Practices_Disclosure_Form.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/156004/4/per2259_am.pd

Is healthy neuroticism associated with longevity? A coordinated integrative data analysis

Early investigations of the neuroticism by conscientiousness interaction with regards to health have been promising, but to date, there have been no systematic investigations of this interaction that account for the various personality measurement instruments, varying populations, or aspects of health. The current study - the second of three - uses a coordinated analysis approach to test the impact of the neuroticism by conscientiousness interaction on the prevalence and incidence of chronic conditions. Using 15 pre-existing longitudinal studies (N > 49,375), we found that conscientiousness did not moderate the relationship between neuroticism and having hypertension (OR = 1.00,95%CI[0.98,1.02]), diabetes (OR = 1.02[0.99,1.04]), or heart disease (OR = 0.99[0.97,1.01]). Similarly, we found that conscientiousness did not moderate the prospective relationship between neuroticism and onset of hypertension (OR = 0.98,[0.95,1.01]), diabetes (OR = 0.99[0.94,1.05]), or heart disease (OR = 0.98[0.94,1.03]). Heterogeneity of effect sizes was largely nonsignificant, with one exception, indicating that the effects are consistent between datasets. Overall, we conclude that there is no evidence that healthy neuroticism, operationalized as the conscientiousness by neuroticism interaction, buffers against chronic conditions

Multiple novel prostate cancer susceptibility signals identified by fine-mapping of known risk loci among Europeans

Genome-wide association studies (GWAS) have identified numerous common prostate cancer (PrCa) susceptibility loci. We have fine-mapped 64 GWAS regions known at the conclusion of the iCOGS study using large-scale genotyping and imputation in 25 723 PrCa cases and 26 274 controls of European ancestry. We detected evidence for multiple independent signals at 16 regions, 12 of which contained additional newly identified significant associations. A single signal comprising a spectrum of correlated variation was observed at 39 regions; 35 of which are now described by a novel more significantly associated lead SNP, while the originally reported variant remained as the lead SNP only in 4 regions. We also confirmed two association signals in Europeans that had been previously reported only in East-Asian GWAS. Based on statistical evidence and linkage disequilibrium (LD) structure, we have curated and narrowed down the list of the most likely candidate causal variants for each region. Functional annotation using data from ENCODE filtered for PrCa cell lines and eQTL analysis demonstrated significant enrichment for overlap with bio-features within this set. By incorporating the novel risk variants identified here alongside the refined data for existing association signals, we estimate that these loci now explain ∼38.9% of the familial relative risk of PrCa, an 8.9% improvement over the previously reported GWAS tag SNPs. This suggests that a significant fraction of the heritability of PrCa may have been hidden during the discovery phase of GWAS, in particular due to the presence of multiple independent signals within the same regio

Adding 6 months of androgen deprivation therapy to postoperative radiotherapy for prostate cancer: a comparison of short-course versus no androgen deprivation therapy in the RADICALS-HD randomised controlled trial

Background Previous evidence indicates that adjuvant, short-course androgen deprivation therapy (ADT) improves metastasis-free survival when given with primary radiotherapy for intermediate-risk and high-risk localised prostate cancer. However, the value of ADT with postoperative radiotherapy after radical prostatectomy is unclear. Methods RADICALS-HD was an international randomised controlled trial to test the efficacy of ADT used in combination with postoperative radiotherapy for prostate cancer. Key eligibility criteria were indication for radiotherapy after radical prostatectomy for prostate cancer, prostate-specific antigen less than 5 ng/mL, absence of metastatic disease, and written consent. Participants were randomly assigned (1:1) to radiotherapy alone (no ADT) or radiotherapy with 6 months of ADT (short-course ADT), using monthly subcutaneous gonadotropin-releasing hormone analogue injections, daily oral bicalutamide monotherapy 150 mg, or monthly subcutaneous degarelix. Randomisation was done centrally through minimisation with a random element, stratified by Gleason score, positive margins, radiotherapy timing, planned radiotherapy schedule, and planned type of ADT, in a computerised system. The allocated treatment was not masked. The primary outcome measure was metastasis-free survival, defined as distant metastasis arising from prostate cancer or death from any cause. Standard survival analysis methods were used, accounting for randomisation stratification factors. The trial had 80% power with two-sided α of 5% to detect an absolute increase in 10-year metastasis-free survival from 80% to 86% (hazard ratio [HR] 0·67). Analyses followed the intention-to-treat principle. The trial is registered with the ISRCTN registry, ISRCTN40814031, and ClinicalTrials.gov, NCT00541047. Findings Between Nov 22, 2007, and June 29, 2015, 1480 patients (median age 66 years [IQR 61–69]) were randomly assigned to receive no ADT (n=737) or short-course ADT (n=743) in addition to postoperative radiotherapy at 121 centres in Canada, Denmark, Ireland, and the UK. With a median follow-up of 9·0 years (IQR 7·1–10·1), metastasis-free survival events were reported for 268 participants (142 in the no ADT group and 126 in the short-course ADT group; HR 0·886 [95% CI 0·688–1·140], p=0·35). 10-year metastasis-free survival was 79·2% (95% CI 75·4–82·5) in the no ADT group and 80·4% (76·6–83·6) in the short-course ADT group. Toxicity of grade 3 or higher was reported for 121 (17%) of 737 participants in the no ADT group and 100 (14%) of 743 in the short-course ADT group (p=0·15), with no treatment-related deaths. Interpretation Metastatic disease is uncommon following postoperative bed radiotherapy after radical prostatectomy. Adding 6 months of ADT to this radiotherapy did not improve metastasis-free survival compared with no ADT. These findings do not support the use of short-course ADT with postoperative radiotherapy in this patient population

Duration of androgen deprivation therapy with postoperative radiotherapy for prostate cancer: a comparison of long-course versus short-course androgen deprivation therapy in the RADICALS-HD randomised trial

Background Previous evidence supports androgen deprivation therapy (ADT) with primary radiotherapy as initial treatment for intermediate-risk and high-risk localised prostate cancer. However, the use and optimal duration of ADT with postoperative radiotherapy after radical prostatectomy remains uncertain. Methods RADICALS-HD was a randomised controlled trial of ADT duration within the RADICALS protocol. Here, we report on the comparison of short-course versus long-course ADT. Key eligibility criteria were indication for radiotherapy after previous radical prostatectomy for prostate cancer, prostate-specific antigen less than 5 ng/mL, absence of metastatic disease, and written consent. Participants were randomly assigned (1:1) to add 6 months of ADT (short-course ADT) or 24 months of ADT (long-course ADT) to radiotherapy, using subcutaneous gonadotrophin-releasing hormone analogue (monthly in the short-course ADT group and 3-monthly in the long-course ADT group), daily oral bicalutamide monotherapy 150 mg, or monthly subcutaneous degarelix. Randomisation was done centrally through minimisation with a random element, stratified by Gleason score, positive margins, radiotherapy timing, planned radiotherapy schedule, and planned type of ADT, in a computerised system. The allocated treatment was not masked. The primary outcome measure was metastasis-free survival, defined as metastasis arising from prostate cancer or death from any cause. The comparison had more than 80% power with two-sided α of 5% to detect an absolute increase in 10-year metastasis-free survival from 75% to 81% (hazard ratio [HR] 0·72). Standard time-to-event analyses were used. Analyses followed intention-to-treat principle. The trial is registered with the ISRCTN registry, ISRCTN40814031, and ClinicalTrials.gov , NCT00541047 . Findings Between Jan 30, 2008, and July 7, 2015, 1523 patients (median age 65 years, IQR 60–69) were randomly assigned to receive short-course ADT (n=761) or long-course ADT (n=762) in addition to postoperative radiotherapy at 138 centres in Canada, Denmark, Ireland, and the UK. With a median follow-up of 8·9 years (7·0–10·0), 313 metastasis-free survival events were reported overall (174 in the short-course ADT group and 139 in the long-course ADT group; HR 0·773 [95% CI 0·612–0·975]; p=0·029). 10-year metastasis-free survival was 71·9% (95% CI 67·6–75·7) in the short-course ADT group and 78·1% (74·2–81·5) in the long-course ADT group. Toxicity of grade 3 or higher was reported for 105 (14%) of 753 participants in the short-course ADT group and 142 (19%) of 757 participants in the long-course ADT group (p=0·025), with no treatment-related deaths. Interpretation Compared with adding 6 months of ADT, adding 24 months of ADT improved metastasis-free survival in people receiving postoperative radiotherapy. For individuals who can accept the additional duration of adverse effects, long-course ADT should be offered with postoperative radiotherapy. Funding Cancer Research UK, UK Research and Innovation (formerly Medical Research Council), and Canadian Cancer Society

New species of Eurythenes from hadal depths of the Mariana Trench, Pacific Ocean (Crustacea: Amphipoda)

Weston, Johanna N. J., Carrillo-Barragan, Priscilla, Linley, Thomas D., Reid, William D. K., Jamieson, Alan J. (2020): New species of Eurythenes from hadal depths of the Mariana Trench, Pacific Ocean (Crustacea: Amphipoda). Zootaxa 4748 (1): 163-181, DOI: https://doi.org/10.11646/zootaxa.4748.1.

Eurythenes plasticus Weston 2020, sp. nov.

<i>Eurythenes plasticus</i> sp. nov. Weston <p>(Figs. 4–8)</p> Material Examined. <p> <b>HOLOTYPE</b>: Mature female, USNM 1615729, body length 48.1 mm.</p> <p> <b>PARATYPES</b>: Mature male, USNM 1615732, GenBank (16S MT 021437), (COI MT 038070), body length 47.6 mm, Mariana Trench, Pacific Ocean (11.5911N, 144.84730E), cruise FK 141109, station LH14, depth 6010 m. Immature female, USNM 1615733 GenBank (16S MT 021438), (COI MT 038071), body length 38.6 mm, Mariana Trench, Pacific Ocean (11.6071N, 144.8331E), cruise FK 141109, station LH15, depth 6142 m. Juvenile, USNM XXXX3, body length 15.6 mm, same collection location as type locality</p> <p>.</p> <p> <b>PARAGENETYPE</b>: Juvenile, GenBank (16S MT 021439), (COI MT 038072), body length 15.1 mm, same collection location as type locality.</p> <p> <b>NON-TYPE SPECIMENS:</b> Three juveniles, body lengths 12.5, 13.5 & 15.7 mm, same collection location as type locality, USNM 1615731.</p> <p> <b>Type Locality.</b> Mariana Trench, Pacific Ocean (12.64065N, 144.73796E), cruise FK141109, station WT02, depth 6865 m.</p> <p> <b>Etymology.</b> The species names, <i>plasticus</i>, stems from Latin for plastic. This name speaks to the ubiquity of plastic pollution present in our oceans.</p> <p> <b>Diagnosis.</b> Lateral cephalic lobe strongly produced, slightly triangular. Article 2 of mandibular palp narrow. Maxilliped inner plate with three to four apical protruding nodular setae. Gnathopod 1 subchelate, basis narrow (2.9x as long as wide), palm not protruding and weakly convex. Gnathopod 2 subchelate, coxa broad ventrally and weakly curved, palm convex. Pereopods 3 to 7 dactyli short. Pereopod 5 coxa bilobate and posterior lobe larger than anterior lobe. Epimeron 3 posteroventral corner subquadrate without small posteroventral tooth. Uropod 1 and 2 rami margins with spine-like setae. Dorsal carination with increasing degree on epimeron 1-3 and urosomite 1.</p> <p> <b>Description, based on holotype, female,</b> USNM 1615729.</p> <p> <b>BODY (Figs. 4, 5, 6):</b> surface smooth, without setae; urosomite 3 with an anterodorsal depression. <i>Oostegites</i> present on gnathopod 2 to pereopod 5, elongate but lacking setae. <i>Coxa gills</i> present on gnathopod 2 to pereopod 7. <i>Colour pattern</i> at time of recovery unknown.</p> <p> <b>HEAD (Fig. 5):</b> rostrum absent; ventral corner of eye rounded and obliquely pointing backwards (Fig. 5C). <i>Antenna 1</i> short, 0.1x as long as body length; accessory flagellum 12-articulate; primary flagellum 28-articulate; callynophore well-developed; calceoli absent (Fig. 5A). <i>Antenna 2</i> medium length, 0.3x as long as body, 1.8x as long as antenna 1; flagellum 59-articulate; calceoli absent (Fig. 5B).</p> <p> <b>MOUTHPART BUNDLE (Fig. 5):</b> <i>Mandible</i> left lacinia mobilis a long slender distally cuspidate robust seta; setal row left with 13 short, slender, robust setae; molar large, setose, vestigial distal triturating patch; palp article length ratio 1: 3.2: 2.6, article 2 posteriorly not expanded and distally not tapering, 3.4x as long as wide; article 3 blade-like (Fig. 5I). <i>Maxilla 1</i> inner plate with nine apical and sub-apical plumose setae; outer plate with an 8/3 setal crown arrangement; palp longer than outer plate, 2-articulate, seven sub-apical and apical setae with one being a flag seta (Fig. 5H). <i>Maxilla 2</i> inner and outer plates broad, inner plate 0.6x shorter than outer plate (Fig. 5G). <i>Maxilliped</i> inner plate large, sub-rectangular, four apical protruding nodular setae; outer plate subovate, with 12 apical setose setae; palp large and well-developed; dactylus well-developed, unguis present, six small apical setae (Fig. 5D, F).</p> <p> <b>PEREON (Figs. 6, 7):</b> <i>Gnathopod 1</i> coxa very weakly anteriorly concave, anteroventral margin with setae; palm crenulate, 0.4x as long as width of propodus, defined by one robust seta at base of palm and another robust seta at end of palm that is 2.6x longer; dactylus curved posteriorly, one long anterodistal seta, unguis present (Fig. 6A, B). <i>Gnathopod 2</i> subchelate, coxa obovate, broad ventrally and weakly curved; propodus elongate, not expanded distally, 6.1x as long as wide; propodus 2.7x as long as wide, moderately expanded distally; palm crenulate, distal end defined by three robust setae; dactylus not reaching palmar corner, curved posteriorly, unguis present, one long anterodistal seta (Fig. 6A, B). <i>Pereopod 3</i> coxa sub-rectangular, 2.0x as long as wide, setae on surface of coxa and along ventral and posterior margins; basis weakly expanded posteriorly, 2.7x as long as wide; merus expanded anteriorly, tuft of setae on anteroventral corner; propodus 4.8x as long as wide; dactylus short, 0.4x as long as propodus, unguis present (Fig. 6C). <i>Pereopod 4</i> coxa broad, 1.2x as long as wide, 1.1x length of coxa 3, junction between anterior and ventral border bluntly angular (sub-rectangular), ventral border straight, posteroventral border straight and weakly oblique; leg almost identical with pereopod 3 (Fig. 6D). <i>Pereopod 5</i> coxa bilobate, posterior lobe 1.3x longer and 1.6x wider than anterior lobe, ventral border of posterior lobe sub-triangular; basis expanded posteriorly, posterior margin smooth; merus broadly expanded posteriorly, 1.5x as long as wide, curved posterior margin; propodus slender, 6.2x as long as wide, seven groups of robust setae on the anterior margin; dactylus short, 0.4x as long as propodus, unguis present (Fig. 7A). <i>Pereopod 6</i> coxa subquadrate, posterior margin weakly bilobate or weakly concave; basis expanded posteriorly, posterior margin distinctly crenate; merus broadly expanded posteriorly, 1.7x as long as wide, convex posterior margin; propodus slender, 5.9x as long as wide, eight groups of robust setae on the anterior margin; dactylus slender, short, 0.3x as long as propodus, unguis present (Fig. 7B). <i>Pereopod 7</i> coxa sub-rectangular; basis with posterior border crenulate and strongly expanded, distal lobe moderately protruding; merus broadly expanded posteriorly, 1.6x as long as wide, convex posterior margin; propodus with normal stoutness, 5.6x as long as wide, eight groups of robust setae on the anterior margin; dactylus slender, short, 0.3x as long as propodus, unguis present (Fig. 7C).</p> <p> <b>PLEON AND UROSOME (Figs. 7, 8):</b> <i>Epimeron 1</i> anteroventral corner rounded with long slender setae; posteroventral corner produced into a small tooth. <i>Epimeron 2</i> anteroventral margin lined with short fine setae; posteroventral corner produced into a strong tooth. <i>Epimeron 3</i> ventral margin lined with long fine setae, weakly curved (Fig. 7D). <i>Urosomite 1</i> with anterodorsal notch (Fig. 7D). <i>Uropod 1</i> peduncle with one apicomedial setae; inner ramus subequal in length to outer ramus; outer ramus 0.85x as long as peduncle; outer ramus with 18 lateral and eight medial spine-like setae; inner ramus with 20 lateral and 11 medial spine-like setae (Fig. 8A). <i>Uropod 2</i> peduncle with one apicomedial setae; inner ramus subequal in length (0.9x) to outer ramus; outer ramus subequal in length to peduncle outer ramus with 20 lateral and three medial spine-like setae; inner ramus with seven lateral and 16 medial spine-like setae (Fig. 8B). <i>Uropod 3</i> inner ramus subequal in length to article 1 of outer ramus; article 2 of outer rami short, 0.05x length of article 1; setae of distolateral angle of peduncle of normal length and stoutness; medial margins of both rami with plumose setae (Fig. 8C). <i>Telson</i> 70% cleft, pair of apical setae on each lobe parallel with beginning of cleft, distal margin with a single apical seta on right lobe, distal end of left lob missing (Fig. 8D).</p> <p> <b>Variations</b>. As with other species of <i>Eurythenes</i>, there appears to be very little sexual dimorphism. In part, this could be limited to having a single male specimen. The mature male paratype (USNM 1615732) has calceoli present on both antenna 1 and antenna 2. Both antennae are shorter than the holotype with antenna 1 accessory flagellum being 10-articulate, antenna 1 25-articulate, and antenna 2 54-articulate. Additionally, the maxilliped inner plate of the male paratype has three apical protruding nodular setae, specifically lacking the third setae present on the holotype (Fig. 5F). There were differences present in the juvenile paratype (USNM 1615730) that included typical cohort differences among <i>Eurythenes</i>, such as fewer setae on pereopods and uropods and reduced articulation on antennae (antenna 1 accessory flagellum 7-articulate, antenna 1 15-articulate, and antenna 2 38-articulate). In addition, the juvenile paratype had more pronounced and raised dorsal carination than on the adults (Fig. 7E). This difference was present among all the juvenile specimens observed.</p> <p> <b>Differential Diagnosis.</b> As highlighted in d’Udekem d’Acoz & Havermans (2015), the morphological characteristics that separate and define the species within the <i>gryllus</i> -complex are hard to observe and should be used with caution. <i>Eurythenes plasticus</i> sp. nov. is a member of the <i>gryllus</i> -complex morphologically and genetically. Nevertheless, there is a combination of characters that are unique to <i>E</i>. <i>plasticus</i> sp. nov. and allow it to be distinguished from the morphologically similar species <i>E. andhakarae</i>, <i>E. magellanicus</i>, and <i>E. aequilatus.</i> The most distinctive characteristics are the robust, spine-like setae on rami of uropod 1 and 2 (Fig. 8A, B) and the lobes of pereopod 5 coxa (Fig. 7A), here being unequal, which is novel within <i>Eurythenes</i>. <i>Eurythenes plasticus</i> sp. nov. can be differentiated from <i>E. andhakarae</i> with article 2 of the mandible palp being narrow (instead of expanded), four protruding nodular spines on the inner plate of the maxilliped (versus three non-protruding), and straight ventral border of coxa 4 (opposed to curved). <i>Eurythenes plasticus</i> sp. nov. can be separated from <i>E. magellanicus</i> with a long gnathopod 1 palm (instead of short), a straight ventral border of coxa 4 (opposed to curved), a subquadrate posteroventral corner in epimeron 3 (instead of bearing a small tooth), and the rami of uropod 1 and 2 being subequal (opposed to uropod 2 outer ramus being shorter than inner ramus and uropod 1 outer ramus being longer than inner ramus). <i>Eurythenes plasticus</i> sp. nov. can also be distinguished from <i>E. aequilatus</i> by its eyes with a variable width (opposed to constant width), the outer plate of maxilla 1 with 8/3 crown arrangement (instead of 9/3 arrangement), and a long gnathopod 1 palm (instead of short).</p> <p> <b>Habitat, Distribution and Biology.</b> <i>Eurythenes plasticus</i> sp. nov. was collected from the upper hadal depths of the Mariana Trench, between 6010 and 6949 m. Similar to sister species within the genus, <i>E. plasticus</i> sp. nov. is a benthic scavenger, as individuals of multiple cohorts entered the baited traps. <i>Eurythenes plasticus</i> sp. nov. is a member of a wider scavenging amphipod community comprised of <i>A. gigantea</i>, <i>Bathycallisoma schellenbergi</i> (Birstein & Vinogradov, 1958), <i>Hirondellea dubia</i> Dahl, 1959, <i>H. gigas</i>, <i>Paralicella caperesca</i> Shulenberger & Barnard, 1976, <i>Paralicella tenuipe</i> s Chevreux, 1908, and <i>Valettietta anacantha</i> (Birstein & Vinogradov, 1963), which were concurrently recovered in the traps (data unpublished).</p> <p> <b>Discussion</b></p> <p> The salient finding of this study is the paired molecular and morphological identification approaches provided congruent evidence that <i>E. plasticus</i> sp. nov. represents an undescribed species within <i>Eurythenes</i>. Further, as a scavenger at upper hadal depths (6010 – 6949 m) in the Mariana Trench, <i>E. plasticus</i> sp. nov. is not exempt from ingesting microplastics that are bioavailable within the hadal zone.</p> <p> In comparison to described <i>Eurythenes</i> species, <i>E</i>. <i>plasticus</i> sp. nov. was placed as part of the <i>gryllus</i> -complex and most closely related to the abyssal <i>E. magellanicus</i> (Fig. 2). The bPTP analysis of COI and both K2P analyses delineated <i>E</i>. <i>plasticus</i> sp. nov. to be a distinctive lineage, and these methods aligned with previous studies that detected cryptic speciation within the <i>gryllus</i> -complex (Havermans <i>et al.</i> 2013; Eustace <i>et al.</i> 2016; Narahara-Nakano <i>et al.</i> 2017). The 16S phylogeny specifically showed <i>E</i>. <i>plasticus</i> sp. nov. to be nearly identical to Eg7 (Fig. 2A; France & Kocher 1996; Havermans <i>et al</i>. 2013). This <i>Eurythenes</i> sp. was a singleton recovered from abyssal depths at the Horizon Guyot seamount, Pacific Ocean, and it was collected along with another <i>Eurythenes</i> sp. from the divergent Eg9 clade (Havermans <i>et al</i>. 2013). Confidence in the identification of Eg7 would be further strengthened with additional genetic or morphological data.</p> <p> The morphological variation seen in <i>E. plasticus</i> sp. nov., such as an uneven coxa 5 lobe and lack of a tooth on the posteroventral corner of epimeron 3, supported the phylogenetic evidence as an undescribed lineage. Consistent with previous studies, these morphological characteristics should be used with caution, as some are difficult to discern objectively. Additional specimens, like from the Eg7 clade, may reveal phenotypic plasticity in the characteristics observed in this morphological study (d’Udekem d’Acoz & Havermans 2015). Continued application of a combined molecular and morphological approaches in future studies is likely to reveal further species diversity within the <i>gryllus</i> -complex.</p> <p> The discovery of <i>E. plasticus</i> sp. nov. continues to align with the pattern <i>Eurythenes</i> that the geographic and bathymetric species distributions are complex (Havermans 2016). With the Eg7 singleton, the geographic range of <i>E. plasticus</i> sp. nov. thus far appears to be restricted to the Central Pacific Ocean. Across that ocean basin, <i>E. plasticus</i> sp. nov. has broad bathymetric range, ~ 3000 m. While it is common among <i>Eurythenes</i> to be found only in a single ocean basin and have a wide vertical distribution (Eustace <i>et al.</i> 2016; Havermans 2016), it is less common to span across the abyssal and hadal zones. Although, this is not unique, as it has been documented in other amphipods, such as <i>A. gigantea</i> (Jamieson <i>et al.</i> 2013). A species needs to be able to cope at the cellular, reproductive, and physiological levels in both the stable abyssal (Smith <i>et al.</i> 2008) and the dynamic hadal environments (Jamieson 2015; Downing <i>et al</i>. 2018). Yet, it was curious that during the present study, <i>E</i>. <i>plasticus</i> sp. nov. was only collected from upper hadal depths, despite amphipods being captured at shallower and deeper depths (43 additional deployments 4506 to 10545 m; data unpublished). This highlights that the distribution of <i>E. plasticus</i> sp. nov. is a patchwork. Further work and sampling will be required to understand the conditions that support the presence of this species.</p> <p> The finding of a microplastic fibre in the hindgut of a juvenile was not unexpected. Deep-sea scavenging amphipods, as an adaption to their food limited environment, indiscriminately consume carrion (Blankenship & Levin 2007) and are known to inadvertently ingest microfibres present in the carrion and sediment (Jamieson <i>et al.</i> 2019). The detection of a microplastic adds to the number of hadal scavenging amphipods, including adult specimens of <i>H. gigas</i> from the Mariana Trench and <i>Eurythenes</i> sp. ‘hadal’ the Peru-Chile Trench (Jamieson <i>et al.</i> 2019), which have been found to have consumed plastic microfibers. Microplastic consumption by a juvenile indicates that scavenging amphipods are potentially ingesting microplastics throughout their life, which could pose acute and chronic health effects. While the ecotoxicological impacts of microplastic exposure has yet to be investigated on deep-sea amphipods, early work on other Malacostraca indicates that the ingestion of polypropylene fibres by the sand crab, <i>Emerita analoga</i>, increases adult mortality and decreases in retention of egg clutches (Horn et al. 2019).</p> <p> This study adds to the growing body of literature on marine organisms ingesting plastic and microfibers (Besseling <i>et al.</i> 2015; Lusher <i>et al.</i> 2015; Bellas <i>et al.</i> 2016; Alomar & Deudero 2017). The microplastic found in the hindgut of <i>E. plasticus</i> sp. nov. was most similar to PET, which is one of the top five most prevalent synthetic plastic polymers produced and discarded globally (Geyer <i>et al.</i> 2017). Without substantial global changes to the life cycle of plastic, from reducing the rate of plastic production to improving waste management (Forrest <i>et al.</i> 2019), plastics and microfibres will continue to be transported to the deep sea and be ubiquitous in the hadal food chain for the foreseeable future.</p>Published as part of <i>Weston, Johanna N. J., Carrillo-Barragan, Priscilla, Linley, Thomas D., Reid, William D. K. & Jamieson, Alan J., 2020, New species of Eurythenes from hadal depths of the Mariana Trench, Pacific Ocean (Crustacea: Amphipoda), pp. 163-181 in Zootaxa 4748 (1)</i> on pages 169-177, DOI: 10.11646/zootaxa.4748.1.9, <a href="http://zenodo.org/record/3697667">http://zenodo.org/record/3697667</a&gt