Eurythenes, S. I. Smith

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 : 76

Updated key to Eurythenes specimens larger than 25 mm

This key is expanded from D’Udekem d’Acoz & Havermans, (2015) and Weston et al. (2021) and the caution of use remains. Character differences can be tough to objectively discern, and certain characteristics can be phenotypically variable between cohorts. Morphology 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 (Chrevreux, 1905)

2 The palm of gnathopod 2 minutely chelate or strongly 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 Weston & Espinosa-Leal in Weston, Espinosa-Leal, Wainwright, Stewart, González, Linley, Reid, Hidalgo, Oliva, Ulloa, Wenzhöfer, Glud, Escribano & Jamieson, 2021.

4. Pereonites 6-7 and epimera 1-3 not dorsally keeled to slightly keeled; pereonites 6-7 and epimera 1-2 dorsally not sigmoid (without anterior concavity), epimeron 3 with distinct anterior concavity......................................... 5 Pereonites 6-7 and epimera 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, 2017 .

6. Article 2 of mandibular palp expanded posteriorly........................................................... 7 Article 2 of mandibular palp not expanded posteriorly........................................................ 8

7. Maxilliped with three 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 or uropod 1 and 2 are shorter than paired inner ramus................................................................................ Eurythenes magellanicus (H. Milne Edwards, 1848)

9. Gnathopod 1 basis length/width ratio narrow (>2.9x as on as a wide)............................................ 10 Gnathopod 1 basis length/width ratio broad (>2.5x as on as a wide. Ventral corner of eye sharp and pointing downwards; maxilliped with 3-4 non-protruding nodular spines).................... Eurythenes gryllus (Lichtenstein in Mandt, 1822)

10. Palm of gnathopod 1 weakly produced protrusion. Gnathopod 2 propodus short and broad. Strong degree of crenulation on the posterior border on pereopods 5-7.................................................................................................... Eurythenes plasticus Weston in Weston, Carrillo-Barragan, Linley, Reid & Jamieson, 2020 Palm of gnathopod 1 well produced protrusion. Gnathopod 2 propodus long and broad. Weak degree of crenulation on the posterior border on pereopods 5-7...................................................... Eurythenes inti sp. nov.