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| Eurythenes plasticus Weston in Weston, Carrillo-Barragan, Linley, et al., 2020. |
Abstract
Eurythenes S. I. Smith in Scudder, 1882 are one of the largest scavenging deep-sea amphipods (max. 154 mm) and are found in every ocean across an extensive bathymetric range from the shallow polar waters to hadal depths. Recent systematic studies of the genus have illuminated a cryptic species complex and highlighted the benefits of using a combination of morphological and molecular identification approaches. In this study, we present the ninth species, Eurythenes plasticus sp. nov., which was recovered using baited traps between the depths 6010 and 6949 m in the Mariana Trench (Northwest Pacific Ocean) in 2014. This new Eurythenes species was found to have distinct morphological characteristics and be a well-supported clade based on sequence variation at two mitochondrial regions (16S rDNA and COI). While this species is new to science and lives in the remote hadal zone, it is not exempt from the impacts of anthropogenic pollution. Indeed, one individual was found to have a microplastic fibre, 83.74% similar to polyethylene terephthalate (PET), in its hindgut. As this species has a bathymetric range spanning from abyssal to hadal depths in the Central Pacific Ocean basin, it offers further insights into the biogeography of Eurythenes.
Keywords: Crustacea, Deep sea, integrated taxonomy, cryptic species, molecular phylogeny, microplastic fibre, pollution
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| Photographs of specimens of Eurythenes plasticus sp. nov.: female holotype from 6865 m (top; USNM 1615729), juvenile paratype from 6865 m (bottom left; USNM 1615730), male paratype from 6010 m (bottom right; USNM 1615732). |
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| Microfibre found within the hindgut of a Eurythenes plasticus sp. nov. individual from 6949 m in the Mariana Trench. |
Systematics:
Order Amphipoda Latreille, 1816
Superfamily Lysianassoidea Dana, 1849
Family Eurytheneidae Stoddart & Lowry, 2004
Genus Eurythenes S. I. Smith in Scudder, 1882
Eurythenes plasticus sp. nov. Weston
Diagnosis. 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.
Etymology. The species names, plasticus, stems from Latin for plastic. This name speaks to the ubiquity of plastic pollution present in our oceans.
Habitat, Distribution and Biology. Eurythenes plasticus 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, E. plasticus sp. nov.
is a benthic scavenger, as individuals of multiple cohorts entered the baited traps. Eurythenes plasticus sp. nov. is
a member of a wider scavenging amphipod community comprised of Alicella gigantea, Bathycallisoma schellenbergi
(Birstein & Vinogradov, 1958), Hirondellea dubia Dahl, 1959, H. gigas, Paralicella caperesca Shulenberger & Barnard, 1976, Paralicella tenuipes Chevreux, 1908, and Valettietta anacantha (Birstein & Vinogradov, 1963), which
were concurrently recovered in the traps (data unpublished).
Johanna N. J. Weston, Priscilla Carrillo-Barragan, Thomas D. Linley, William D. K. Reid and
Alan J. Jamieson. 2020. New Species of Eurythenes from Hadal Depths of the Mariana Trench, Pacific Ocean (Crustacea: Amphipoda). Zootaxa. 4748(1); 163–181. DOI: 10.11646/zootaxa.4748.1.9
