Eurythenes atacamensis, Weston & Espinosa-Leal & Wainwright & Stewart & González & Linley & Reid & Hidalgo & Oliva & Ulloa & Wenzhöfer & Glud & Escribano & Jamieson, 2021

Weston, Johanna N. J., Espinosa-Leal, Liliana, Wainwright, Jennifer A., Stewart, Eva C. D., González, Carolina E., Linley, Thomas D., Reid, William D. K., Hidalgo, Pamela, Oliva, Marcelo E., Ulloa, Osvaldo, Wenzhöfer, Frank, Glud, Ronnie N., Escribano, Rubén & Jamieson, Alan J., 2021, Eurythenes atacamensis sp. nov. (Crustacea: Amphipoda) exhibits ontogenetic vertical stratification across abyssal and hadal depths in the Atacama Trench, eastern South Pacific Ocean, Marine Biodiversity 51 (51), pp. 1-20: 6-11

publication ID

http://doi.org/ 10.1007/s12526-021-01182-z

publication LSID

lsid:zoobank.org:pub:086134F0-E428-4C07-AE26-6BC075AF40EB

DOI

http://doi.org/10.5281/zenodo.5841932

persistent identifier

http://treatment.plazi.org/id/51F715E8-AD60-403C-B39A-06F3A3223935

taxon LSID

lsid:zoobank.org:act:51F715E8-AD60-403C-B39A-06F3A3223935

treatment provided by

Felipe

scientific name

Eurythenes atacamensis
status

sp. nov.

Eurythenes atacamensis   sp. nov. Weston & Espinosa-Leal

( Figures 2–6 View Fig View Fig View Fig View Fig View Fig )

http://zoobank.org/51F715E8-AD60-403C-B39A-06F3A3223935

Eurythenes gryllus   — Ingram and Hessler 1987: 1889.— Thurston et al. 2002: 205–210, figs. 1–7, table 1.— Jamieson et al. 2019: 1–9, fig. 1, table 1.

Eurythenes gryllus Peru-Chile   (H)— Ritchie et al. 2015: 121–129, figs.2, 4, tables 1, 2.

Eurythenes sp.   (Hadal Form)— Eustace et al. 2016: 91–97, fig. 1, fig. 2 (d)(e)(f), fig. 5, tables 2, 3.

Material Examined.

Holotype: Female, total body length 76.2 mm, Atacama Trench, eastern South Pacific Ocean (23° 22.774′ S, 71° 20.683′ W), expedition SO216, station 4, depth 8052 m, MNHNCL AMP-15816, genseq-1 16S ( MW042884), COI ( MW048996). GoogleMaps  

Paratypes: Female, total body length 70 mm, Atacama Trench, Pacific Ocean (23° 24.48′ S, 71° 19.91′ W), Atacamex Expedition, station 2, depth 8081 m, MZUC/UCCC 46674   . Female, total body length 72 mm, Atacama Trench, Pacific Ocean (23° 24.48′ S, 71° 19.91′ W), Atacamex Expedition, station 2, depth 8081 m, MZUC/UCCC 46675, genseq-2 16S (MW290039), COI (MW288146)   . Male, total body length 50.8 mm, Atacama Trench, Pacific Ocean (23° 22.384′ S, 71° 23.577′ W), expedition SO216, station 4, depth 7204 m, MNHNCL AMP-15817   . Female, type locality, MNHNCL AMP-15822   . Intersex, total body length 58.8 mm, Atacama Trench, Pacific Ocean (24° 16.233′ S, 71° 25.386′ W), expedition SO216, station 6, depth 7834 m, MNHNCL AMP-15820, genseq-2 16S (MW042883)   . Juvenile, total body length 16.1 mm, Atacama Trench, Pacific Ocean (21° 44.497′ S, 71° 15.465′ W), expedition SO216, station 2, depth 6738 m, MNHNCL AMP-15819   . Juvenile, total body length 38.4 mm, Atacama Trench, Pacific Ocean (21° 44.497′ S, 71° 15.465′ W), expedition SO216, station 2, depth 6714 m, MNHNCL AMP-15818   . Juvenile, Atacama Trench, Pacific Ocean (22° 56.282′ S, 71° 40.686′ W), expedition SO216, station 7, depth 4974 m, MNHNCL AMP-15821   .

Paragenetype: Juvenile, Atacama Trench, Pacific Ocean (22° 56.282′ S, 71° 40.686′ W), expedition SO216, station 7, depth 4974 m, genseq-2 16S (MW042880)   . Juvenile, Atacama Trench, Pacific Ocean (20° 20.608′ S, 71° 07.821′ W), expedition SO216, station 10, depth 5920 m, genseq-2 16S (MW042881), COI (MW048993)   . Female, Atacama Trench, Pacific Ocean (23° 02.998′ S, 71° 15.044′ W), expedition SO216, station 3, depth 7139 m, genseq-2 16S (MW042882), COI (MW048994)   .

Type Locality. Atacama Trench, eastern South Pacific Ocean   GoogleMaps (23° 22.774′ S, 71° 20.683′ W), expedition SO216, station 4, depth 8052 m.

Etymology. The species name, atacamensis   , references the type locality, Atacama Trench, of this conspicuously abundant scavenging amphipod.

Diagnosis. Lateral cephalic lobe rounded and weakly pronounced. Ventral corner of the eye points linearly downwards. Article 2 of mandibular palp expanded posteriorly but not distally tapering. Maxilliped inner plate with three apical, non-protruding nodular setae. Gnathopod 1 subchelate; palm weakly formed, short. Gnathopod 2 minutely chelate; coxa sub-rectangular and posterior margin slightly rounded; palm obtusely angled. Pereopods 3 to 7 dactylus short. Epimeron 3 ventral margin rounded with a small tooth on the posteroventral corner. Uropod 2 inner ramus longer than outer ramus. Lack of dorsal carination or ridging, specifically at pereonite 3.

Description, based on holotype, female, MNHNCL AMP-15816.

Body ( Fig. 2 View Fig ): surface smooth, without setae; urosomite 3 with an anterodorsal depression. Oostegites present on gnathopod 2 to pereopod 5, setae absent. Coxa gills present on gnathopod 2 to pereopod 7. Colour pattern before ethanol preservation unknown as the holotype was selected post-expedition.

Head ( Fig. 3 View Fig ): rostrum absent; antennal sinus quadrate ( Fig. 3d View Fig ). Antenna 1 short, 0.13× as long as body length; accessory flagellum 14-articulate; primary flagellum 34- articulate; calceoli absent ( Fig. 3a View Fig ). Antenna 2 2.4× the length of antenna 1, 0.25× as long as body; article 4–5 with brush setae; flagellum 68-articulate with some brush setae; calceoli absent ( Fig. 3b View Fig ).

Mouthpart bundle ( Fig. 3 View Fig ): Mandible left lacinia mobilis a long slender robust seta with smooth distal margin; incisor smooth and convex; setal row with 11 short, slender, robust setae; molar large, setose, small triturating surface; palp article-length ratio 1: 1.8: 1.6, article 3 sickle-shaped ( Fig. 3c View Fig ). Maxilla 1 inner plate with nine apical plumose setae; outer plate with an 8/3- crown arrangement; palp longer than the outer plate, 2- articulate, four apical and one apicolateral robust setae, with one subapical long setae ( Fig. 3e–h View Fig ). Maxilla 2 both plates broad, inner plate 0.6 × shorter than the outer plate ( Fig. 3i View Fig ). Maxilliped inner plate subrectangular, three apical, non-protruding nodular setae; outer plate subovate; palp 4-articulate, left and right are asymmetric with right palp exceeding past the outer plate, dactylus well-developed, unguis present ( Figure 3j–l View Fig ).

Pereon ( Figs. 4 View Fig and 5 View Fig ): Gnathopod 1 coxa sub-quadrate, weakly concave on anterior and ventral margins; basis, long, length 2.2× breadth; palm weakly formed and short (0.1× as long as the posterior margin of propodus), crenulate with one robust seta at base of the palm and another at the end of palm ( Fig. 4a–b View Fig ). Gnathopod 2 coxa with setae along the posteroventral corner; basis elongate, length 6.9 times width, setae along posterior and ventral margins; posterior margin of merus expanded; propodus sub-rectangular, length 4.5 times width; palm with 2 robust setae on the posterodistal corner; dactylus not reaching palmar corner ( Fig. 4c–d View Fig ). Pereopod 3 coxa sub-quadrate, 1.5× as long as wide, setae on the surface of coxa and along ventral margin; basis expanded posteriorly, 2.3× as long as wide; merus expanded anteriorly, tuft of setae on the anteroventral corner; carpus stout, 0.6× as long as propodus; propodus 3.9× as long as wide; dactylus slender, short 0.3× as long as propodus, unguis present ( Fig. 4e View Fig ). Pereopod 4 coxa broad, 0.9× as long as wide, 1.1× length of coxa 3, the junction between anterior and ventral border bluntly angular (sub-rectangular), ventral border straight, posteroventral border weakly oblique; leg almost identical to pereopod 3 ( Fig. 4f View Fig ). Pereopod 5 coxa sub-rectangular, rounded on both the anterior and posterior margins; basis expanded posteriorly, posterior margin weakly crenulated; merus broadly expanded posteriorly, 1.5× as long as wide, posteroventral margin producing a point; carpus stout, 0.4× as long as propodus; propodus long and slender, 5.5× as long as wide, 11 groups robust setae along anterior margin; dactylus short, 0.4× as long as propodus, unguis present ( Fig. 5a View Fig ). Pereopod 6 coxa sub-rectangular, setae along the ventral margin, posterior margin straight; basis expanded posteriorly with posterior margin crenulated; merus expanded posteriorly, 1.5× as long as wide, convex posterior margin; propodus and dactylus nearly identical to pereopod 5 ( Fig. 5b View Fig ). Pereopod 7 coxa sub-rectangular; basis expanded posteriorly, posterior margin distinctly crenulated, distal lobe weakly protruding; merus broad and strongly expanded posteriorly, subequal length to width; propodus and dactylus nearly identical to pereopod 5 ( Fig. 5c View Fig ).

Pleon and urosome ( Fig. 5 View Fig ): Epimeron 1 with setae along the anteroventral corner ( Fig. 5d View Fig ). Epimeron 2 with setae along the ventral margin, posteroventral corner produced into a strong tooth ( Fig. 5d View Fig ). Epimeron 3 ventral margin rounded with a small tooth on the posteroventral corner ( Fig. 5d View Fig ). Uropod 1 peduncle with 1 apicomedial seta, rami subequal, outer ramus 0.8× as long as peduncle ( Fig. 5e View Fig ). Uropod 2 peduncle with 2 apicomedial setae, outer ramus subequal in length to peduncle, inner ramus longer than outer ramus (1.2×; Fig. 5f View Fig ). Uropod 3 setae of the distolateral angle of peduncle of normal length and stoutness; inner ramus subequal in length to article 1 of the outer ramus; outer rami article 2 0.8× the length of article 1, medial margins of both rami with plumose setae ( Fig. 5g View Fig ). Telson 77% cleft, distal margin of each lobe with one robust and one slender setae ( Fig. 5h–i View Fig ).

Variations. Prior to ethanol preservation, body colour of specimens ranged from white, pink, crimson, to dark red and the eye shape and colour were more defined ( Fig. 6 View Fig ). This wide variation in body pigmentation is likely attributed to the moult/intermoult cycle (Baldwin and Smith 1987). Minor differences were observed between females and the male. The mature male paratype (MNHNCL AMP-15817) had calceoli present on both antennas 1 and 2. The primary flagellum of antenna 1 was 31-articulate with calceoli present between articles 8 and 20, and the accessory flagellum was 12-articulate. Antenna 2 was 65-articulate. The intersex paratype (MNHNCL AMP-15820) had protruding penile papillae that flexed towards each other but lacked calceoli on antenna 1 or 2. As with the holotype, the oostegites were present on pereopod 2–5; however, the flattened oostegites were not of full length relative to the total body length and lacked setae. Moderate differences were present between sexed and juvenile specimens, with fewer setae on pereopods and uropods and a reduction in articulation on antennae. Specifically, in the juvenile paratype (MNHNCL AMP-15818), the antenna 1 accessory flagellum was 10- articulate, antenna 1 was 26-articulate, and antenna 2 was 57-articulate. Further, the juvenile had more pronounced crenulation of the posterior margin of the basis on pereopods 5–7.

Feeding and distribution. This species is a benthopelagic scavenger, which is well documented by its rapid aggregation and feeding at baited the camera landers ( Fig. 6a View Fig ; Hessler et al. 1978). As with Eurythenes plasticus   , individuals of E. atacamensis   sp. nov. have been previously documented to ingest microplastics ( Jamieson et al. 2019; Weston et al. 2020a). Eurythenes atacamensis   sp. nov. has a wide bathymetric range (>3000 m) across abyssal to hadal depths (4974–8081 m), including the deepest point of the Atacama Trench. This species is considered to have a distribution localized to both sectors of the Peru-Chile Trench. Eurythenes atacamensis   sp. nov. is a prominent member of a wider scavenging amphipod community ( Fujii et al. 2013). This community is comprised of three species also endemic to the Peru-Chile Trench, Hirondellea thurstoni Kilgallen, 2015   , Hirondellea sonne Kilgallen, 2015, and Hirondellea wagneri Kilgallen, 2015.

Differential diagnosis. In a genus with cryptic speciation ( Havermans et al. 2013), Eurythenes atacamensis   sp. nov. has distinct diagnostic features. These features include a smooth dorsal body, the palm of gnathopod 1 being very short, and the palm of gnathopod 2 being minutely chelate with an obtusely angled palm. Eurythenes atacamensis   sp. nov. is the most similar morphologically to Eurythenes thurstoni Stoddart & Lowry, 2004   , as they both have a minutely chelate gnathopod 2. Yet, E. atacamensis   sp. nov. can be readily differentiated by the lack of an upturned ridge on the anterodorsal margin of head (present in E. thurstoni   ), uropod 2 inner ramus longer than outer ramus (opposed to subequal), and small tooth on the posteroventral corner of epimeron 3 (versus subquadrate). Eurythenes thurstoni   is also smaller in total body size, most commonly not longer than 35 mm ( Stoddart and Lowry 2004). Additionally, the two species have a disjunct vertical distribution, where E. thurstoni   lives at bathyal depths ( Stoddart and Lowry 2004; d’ Udekem d’ Acoz and Havermans 2015).

Kingdom

Animalia

Phylum

Arthropoda

Class

Malacostraca

Order

Amphipoda

Family

Eurytheneidae

Genus

Eurythenes

Loc

Eurythenes atacamensis

Weston, Johanna N. J., Espinosa-Leal, Liliana, Wainwright, Jennifer A., Stewart, Eva C. D., González, Carolina E., Linley, Thomas D., Reid, William D. K., Hidalgo, Pamela, Oliva, Marcelo E., Ulloa, Osvaldo, Wenzhöfer, Frank, Glud, Ronnie N., Escribano, Rubén & Jamieson, Alan J. 2021
2021
Loc

Eurythenes sp.

Eustace RM & Kilgallen NM & Ritchie H & Piertney SB & Jamieson AJ 2016: 91
2016
Loc

Eurythenes gryllus

Ritchie H & Jamieson AJ & Piertney SB 2015: 121
2015
Loc

Eurythenes gryllus

Jamieson AJ & Brooks LS & Reid WD & Piertney SB & Narayanaswamy BE & Linley TD 2019: 1
Thurston MH & Petrillo M & Della Croce N 2002: 205
Ingram CL & Hessler RR 1987: 1889
1987