Eurythenes inti, Wainwright & Weston & Bond & Jamieson, 2025

Wainwright, Jennifer A., Weston, Johanna N. J., Bond, Todd & Jamieson, Alan J., 2025, A new species of Eurythenes (Crustacea: Amphipoda) from abyssal depths in the Peru-Chile Trench., Zootaxa 5653 (1), pp. 63-79 : 69-75

Eurythenes inti sp. nov. Wainwright & Weston, 2025 in Wainwright, Weston, Bond & Jamieson 2025.

ZooBank ID. urn:lsid:zoobank.org:pub:FFF28548-FFE4-4C59-85B2-DE3D6D3FF2CE

Eurythenes sp. Abyssal-major— Ritchie et al. (2015): 121–129, figs.2, 4, tables 1, 2.

Eurythenes sp. abyssal morph— Eustace et al. (2016): 91-98, figs. 1, 2, 3, 4, 5, table 3.

Eurythenes sp. abyssal major— Havermans, (2016): 12-25, figs. 2, 3, 4, table 2.

Eurythenes sp. ‘PCT abyssal’— Weston et al. (2020): 163-181, figs. 2, table 2. Weston et al. (2021): figs. 7, table 2.

Eurythenes sp. abyssal— Horton et al. (2020): figs. 4,6, table 2.

Material Examined.

Holotype: Mature male, total body length 55.6 mm, MNHNCL AMP-15979 .

Paratypes: Mature male, 48.2 mm, MNHNCL AMP-15980 . Peru-Chile Trench, eastern south Pacific 06° 12.42’ S, 81°40.13’ W, Expedition SO209, station number 11, 4602 m.

Type Locality. Peru-Chile Trench, eastern south Pacific Ocean 06° 12.42’ S, 81°40.13’ W, Expedition SO209, station number 3, 5329 m.

Etymology. “ Inti” refers to the Quechua word for Sun. Quechua was the language of the ancient Inca people of South America who lived in Peru and Chile. The sun refers to both the German Vessel Sonne on which this species was discovered, and the white to pale pink colour of the amphipod’s exoskeleton.

Diagnosis. Coxa 1 sub-square tapering anteriorly. Gnathopod 1 subchelate with well-developed, transverse palm. Coxa 2 anteriorly rounded. Gnathopod 2 subchelate with convex palm. Uncarinated dorsal ridge produced from pereonite 5 to urosomite 1. Ventral corner of eye blunt, pointing obliquely backwards. Article 2 of mandibular palp weakly expanded posteriorly but not distally tapering. Maxilliped inner plate with three apical, non-protruding nodular setae. Pereopods 3 to 7 dactylus short. Uropod 2 inner ramus 0.9x the length of the outer ramus. Epimeron 2 posteroventral corner produced into a small tooth. Epimeron 3 posteroventral corner rounded.

Description based on holotype, male, 55.6 mm, MNHNCL AMP-15979.

Body. Surface smooth without setae. Pereonite dorsal ridging from pereonite 5 to urosomite 1, not carinated. Penile papillae present on the sternite of pereopod 7. Coxa gills present on gnathopod 2 to pereopod 7. Colour pattern of holotype before preservation unknown.

Head. Rostrum absent. Lateral cephalic lobe strongly produced, slightly triangular. Antenna 1 medium length, 0.2× body length, 38 articulate, article 1 3.1x the length of article 2 and 3, accessory flagellum 15-articulate, calceoli absent. Antenna 2 broken at article 4.

Mouthpart bundle. Mandible lacinia mobilis present on the left and right; slender and smooth; setal row with 11 robust setae; incisor smooth and straight, left and right symmetrical; palp 3-articulate attached centrally, article 3 0.75x the length of article 2 and weakly sickle-shaped; molar rounded with no triturating surface. Maxilla 1 outer plate with an 8/3 crown arrangement; palp reaching the top of the teeth on the outer plate, 2-articulate, three robust setae, and two flag setae. Maxilla 2 both plates broad with slender setae, inner plate 0.6x shorter than outer plate. Maxilliped symmetrical, palp 4-articulate, dactylus well-developed; outer plate large, reaching almost the top of palp article 2, with strong, well-developed robust setae along apical and inner margin; symmetrical inner plates, apically square with three apical non-protruding nodular setae and a row of 14 slender setae, inner margin with slender plumose setae. Epistome and upper lip separate.

Pereon. Gnathopod 1 coxa sub-square tapering anteriorly, basis long with brush setae on anterior margin, length 3.0× breadth; propodus margins subparallel; palm subchelate with well-developed, transverse palm, denticulate with one large, robust seta at posterodistal corner, and one smaller robust seta at base of dactylus; dactylus 1.7x longer than palm. Gnathopod 2 coxa small and round, tapering posteriorly; basis long, length 6x breadth; posterior margin of merus expanded with brush setae; carpus and propodus with posterior and anterior setae; propodus length 3x breadth; palm subchelate with convex palm, with three robust setae on the posterodistal corner; dactylus not reaching palmar corner. Pereopod 3 coxa rectangular with rounded margins, 2× as long as wide; basis slightly expanded posteriorly, 2.7× as long as wide; merus slightly expanded anteriorly, carpus 1.6x the length of the propodus; dactylus slender length 0.5× the length of the propodus. Pereopod 4 coxa wide and broad, length 1.2× width; anteroventral border weakly oblique, ventral border weakly convex, posteroventral border weakly oblique; leg almost identical to pereopod 3. Pereopod 5 coxa sub-rectangular and weakly bilobate, rounded on both the anterior and posterior margins; basis expanded posteriorly; merus broadly expanded posteriorly, length 1.2× width, carpus short, 0.3× as long as propodus; propodus long, length 6.7× width, nine groups of robust setae along posterior margin; dactylus short, 0.3× propodus. Pereopod 6 coxa sub-square, smaller than coxa 5; basis expanded posteriorly with posterior margin crenulated; merus broadly expanded posteriorly, length 1.4× width; propodus and dactylus nearly identical to pereopod 5. Pereopod 7 coxa sub-rectangular; basis with posterior expansion, crenulated posterior-ventral margin, length 1.3× width; merus broadly expanded posteriorly, length to width subequal; propodus and dactylus nearly identical to pereopod 5 and 6.

Pleon and urosome. Epimeron 1 posteroventral margin produced to a corner. Epimeron 2 posteroventral corner produced into a small tooth. Epimeron 3 posteroventral corner rounded.

Uropod 1 peduncle with 1 robust apicomedial seta, rami subequal, outer ramus 0.7× as long as peduncle with robust setae. Uropod 2 peduncle with 1 apicomedial setae, inner rami 0.9× the length of outer ramus, outer ramus as long as peduncle. Uropod 3 peduncle with plumose setae, rami subequal, outer ramus 2× the length of peduncle, second article missing. Telson deeply cleft (85%), small surface setae, two apical setae.

Variations. Paratype Male. Antenna 2 long, 86 articulate, 2× the length of antenna 1, 0.25× body length, calceoli absent. Colour Amphipods were qualitatively documented with colour ranging from white to light red.

Feeding and distribution. This species is a benthopelagic scavenger that can rapidly detect and swarm baited traps. Eurythenes inti sp. nov. has an abyssal to shallow hadal distribution, spanning around 1500 m (~4602–~ 6173 m water depth). So far collected only from the Milne-Edwards sector of the Peru-Chile Trench ( Eustace et al. 2016).

Differential diagnosis. Previous studies have documented Eurythenes inti sp. nov. to be genetically most closely related to E. magellanicus , E. aequilatus , and E. plasticus ( Ritchie et al. 2015; Weston et al. 2021). Eurythenes inti sp. nov. can be distinguished from these three species by the uncarinated dorsal ridge produced from pereonite 5 to urosomite 1. Eurythenes magellanicus has slightly longer ridging from pereonite 3 to urosomite 1 with slight carination. Eurythenes aequilatus and E. plasticus do not have dorsal ridges. Additionally, the shape of coxa 2 of Eurythenes inti sp. nov. is small and rounded, tapering posteriorly, whereas E. magellanicus and E. plasticus have much broader coxa 2. Eurythenes aequilatus coxa 2 is sub-rectangular.

Eurythenes inti sp. nov. shares its distribution with at least E. magellanicus in the Milne-Edwards Trench. However, due to the sporadic nature of deep-sea sampling the full geographic distributions of all Eurythenes species remains unknown. Further sampling may reveal more species with sympatric distributions. Eurythenes inti sp. nov. can be further distinguished from E. magellanicus by the rounded epimeron 3 which can be produced to a tooth in E. magellanicus , and the three non-protruding nodular spines on the inner plate of the maxilliped (4 to 6 protruding nodular spines in E. magellanicus ). These features should be used with caution as the tooth on the epimeron 3 of E. magellanicus is known to be variable with size, and the number of non-protruding nodular spines can vary ontogenetically within a species ( D’Udekem D’acoz & Havermans, 2015). Eurythenes inti sp. nov. also shares its distribution with E. atacamensis and can be most easily distinguished from this species by the shape of gnathopod 2 palm. Eurythenes inti sp. nov. is sub-chelate, while minutely chelate in E. atacamensis .

Morphological species matrix. The key morphological characters that may be used to distinguish each Eurythenes species from the rest are presented in a species matrix table ( Table 2 ). These features were first identified by Havermans et al. (2013) then updated by D’Udekem d’Acoz & Havermans, (2015) and recommended to be used alongside the key to Eurythenes for morphological identifications of these cryptic species.