Eurythenes atacamensis sp. nov. (Crustacea: Amphipoda) exhibits ontogenetic vertical stratification across abyssal and hadal depths in the Atacama Trench, eastern South Pacific Ocean Author Weston, Johanna N. J. 0000-0002-7142-3081 School of Natural and Environmental Sciences, Newcastle University, Newcastle Upon Tyne NE 1 7 RU, UK j.weston2@newcastle.ac.uk Author Espinosa-Leal, Liliana 0000-0003-2099-8376 Programa de Doctorado en Oceanografía, Departamento de Oceanografía, Universidad de Concepción, P. O. Box 160 C, Concepción, Chile & Departamento de Oceanografía and Instituto Milenio de Oceanografía, Universidad de Concepción, P. O. Box 160 C, Concepción, Chile lespinosa@udec.cl Author Wainwright, Jennifer A. School of Natural and Environmental Sciences, Newcastle University, Newcastle Upon Tyne NE 1 7 RU, UK Author Stewart, Eva C. D. 0000-0001-8383-5705 School of Natural and Environmental Sciences, Newcastle University, Newcastle Upon Tyne NE 1 7 RU, UK & Life Sciences, The Natural History Museum, Cromwell Road, London SW 7 5 BD, UK Author González, Carolina E. 0000-0002-9415-2501 Departamento de Oceanografía and Instituto Milenio de Oceanografía, Universidad de Concepción, P. O. Box 160 C, Concepción, Chile Author Linley, Thomas D. 0000-0002-6583-3105 School of Natural and Environmental Sciences, Newcastle University, Newcastle Upon Tyne NE 1 7 RU, UK Author Reid, William D. K. 0000-0003-0190-0425 School of Natural and Environmental Sciences, Newcastle University, Newcastle Upon Tyne NE 1 7 RU, UK Author Hidalgo, Pamela 0000-0002-5872-7574 Departamento de Oceanografía and Instituto Milenio de Oceanografía, Universidad de Concepción, P. O. Box 160 C, Concepción, Chile Author Oliva, Marcelo E. 0000-0003-1759-2797 Instituto de Ciencias Naturales Alexander von Humboldt, Facultad de Ciencias del Mar y Recursos Biológicos, Universidad de Antofagasta, Antofagasta, Chile Author Ulloa, Osvaldo 0000-0002-9501-5576 Departamento de Oceanografía and Instituto Milenio de Oceanografía, Universidad de Concepción, P. O. Box 160 C, Concepción, Chile Author Wenzhöfer, Frank 0000-0002-4621-0586 HGF-MPG Group for Deep Sea Ecology and Technology, Alfred-Wegener-Institute Helmholtz-Center for Polar and Marine Research, 27570 Bremerhaven, Germany & Max Planck Institute for Marine Microbiology, 28358 Bremen, Germany & Department of Biology, Nordcee and HADAL, University of Southern Denmark, 5230 Odense M, Denmark Author Glud, Ronnie N. 0000-0002-7069-893X Department of Biology, Nordcee and HADAL, University of Southern Denmark, 5230 Odense M, Denmark & Tokyo University of Marine Science and Technology, 4 - 5 - 7 Konan, Minato-ku, Tokyo 108 - 8477, Japan Author Escribano, Rubén 0000-0002-9843-7723 Departamento de Oceanografía and Instituto Milenio de Oceanografía, Universidad de Concepción, P. O. Box 160 C, Concepción, Chile Author Jamieson, Alan J. 0000-0001-9835-2909 School of Natural and Environmental Sciences, Newcastle University, Newcastle Upon Tyne NE 1 7 RU, UK text Marine Biodiversity 2021 2021-05-14 51 51 1 20 http://dx.doi.org/10.1007/s12526-021-01182-z journal article 10.1007/s12526-021-01182-z 2368ec8a-ba39-4a8f-bc34-69b5857ba965 PMC8120496 34007343 5841926 086134F0-E428-4C07-AE26-6BC075AF40EB Key to Eurythenes specimens larger than 25 mm. This key is expanded from d’ Udekem d’ Acoz and Havermans (2015) , and the caution of use remains. Character differences can be tough to objectively discern, and certain characteristics can be phenotypically variable between cohorts. Visual identification paired with DNA barcoding is strongly recommended. 1. Dactylus of pereopods 3–7 short (less than 0.3 of propodus)....................................................................................................2 Dactylus of pereopods 3–7 long (more than 0.6 of propodus).......................................... Eurythenes obesus ( Chevreux, 1905 ) 2. The palm of gnathopod 2 minutely chelate or very protruding.................................................................................................3 The palm of gnathopod 2 subchelate or weakly protruding......................................................................................................4 3. The anterodorsal margin of the head forming an upturned ridge; posterodistal lobe of the basis of pereopod 7 very long...................................................................................................................... Eurythenes thurstoni Stoddart & Lowry, 2004 The anterodorsal margin of the head not forming an upturned ridge; palm of gnathopod 1 very short; posterodistal lobe of the basis of pereopod 7 short or fairly short................................................................................. Eurythenes atacamensis sp. nov. 4. Pereopods 6–7 and epimerons 1–3 not dorsally keeled to slightly keeled; pereopods 6–7 and epimerons 1–2 dorsally not sigmoid (without anterior concavity), epimeron 3 with distinct anterior concavity..................................................................5 Pereopods 6–7 and epimerons 1–3 dorsally strongly keeled and sigmoid (anteriorly slightly to distinctly concave)................................................................................... Eurythenes sigmiferus d’ Udekem d’ Acoz & Havermans, 2015 5. Eyes of variable width; the outer plate of maxilla 1 with 8/3 crown arrangement...................................................................6 Eyes of constant width; the outer plate of maxilla 1 with 9/3 crown arrangement.............................................................. Eurythenes aequilatus Narahara-Nakano, Nakano & Tomikawa, 2018 6. Article 2 of mandibular palp moderately to strongly expanded posteriorly..............................................................................7 Article 2 of mandibular palp not to weakly expanded posteriorly............................................................................................8 7. Maxilliped with 3 non-protruding nodular spines; pereopod 7 with basis posteriorly strongly expanded, with merus narrow..................................................................................... Eurythenes andhakarae d’ Udekem d’ Acoz & Havermans, 2015 Maxilliped with 8–9 non-protruding nodular spines; pereopod 7 with basis posterior border weakly expanded, with merus stout........................................................................................... Eurythenes maldoror d’ Udekem d’ Acoz & Havermans, 2015 8. Gnathopod 2 palm convex; uropod 1 and 2 rami subequal.......................................................................................................9 Gnathopod 2 palm straight; the outer ramus of uropod 1 and 2 are shorter than paired inner ramus......................................................................................................... Eurythenes magellanicus (H. Milne Edwards, 1848 ) 9. Ventral corner of eye rounded and obliquely pointing backward; maxilliped with 3–4 protruding nodular spines; gnathopod 1 palm convex....................................................................................................................… Eurythenes plasticus Weston, 2020a Ventral corner of eye sharp and pointing downward; maxilliped with 3–4 non-protruding nodular spines; gnathopod 1 palm straight…........................................................................................................ Eurythenes gryllus (Lichtenstein in Mandt, 1822)