Eurythenes

D’Acoz, Cédric D’Udekem & Havermans, Charlotte, 2015, Contribution to the systematics of the genus Eurythenes S. I. Smith in Scudder, 1882 (Crustacea: Amphipoda: Lysianassoidea: Eurytheneidae), Zootaxa 3971 (1), pp. 1-80 : 9-10

Key to Eurythenes specimens larger than 25 mm

This key should be used with caution, for three reasons: (1) some characters are hard to observe, (2) material examined was limited and (3) the analysis of DNA sequences of specimens not examined morphologically strongly suggests the existence of further, undescribed species.

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)............................................ E. obesus

2. Anterodorsal margin of head not forming an upturned ridge; palm of gnathopod 2 not or weakly protruding; junction between ventral and posteroventral border of coxa 4 distinct; posterodistal lobe of basis of pereopod 7 short or fairly short; pleonite 3 notched dorsally...................................................................................... 3

- Anterodorsal margin of head forming an upturned ridge; palm of gnathopod 2 very protruding; junction between ventral and posteroventral border of coxa 4 indistinct; posterodistal lobe of basis of pereopod 7 very long; pleonite 3 not notched dorsally, showing only a scarcely distinct concavity........................................................ E. thurstoni

3. Coxa 2 ventrally broad and weakly curved................................................................. 4

- Coxa 2 ventrally narrow and strongly curved....................................................... E. maldoror

4. Pereonites 6–7 and pleonites 1–3 not keeled to slightly keeled; pereonites 6–7 and pleonite 1–2 dorsally not sigmoid (without anterior concavity), pleonite 3 with distinct anterior concavity.................................................. 5

- Pereonites 6–7 and pleonites 1–3 strongly keeled and sigmoid (anteriorly slightly to distinctly concave)....... E. sigmiferus

5. Anterior lobe of head protruding; lower lobe of eye rounded and pointing obliquely backwards; inner plate of maxilliped with 3 to 6 nodular spines.................................................................................. 6

- Anterior lobe of head not protruding; lower lobe of eye acute and pointing downwards; inner plate of maxilliped with 3 (sometimes 4 on one side) nodular spines................................................................ E. gryllus

6. Maxilliped with 3 non-protruding nodular spines; pereopod 7 with basis posteriorly strongly expanded, with merus narrow........................................................................................... E. andhakarae

- Maxilliped with 4–6 protruding nodular spines; pereopod 7 with basis posteriorly not strongly expanded, with merus rather stout.................................................................................... E. magellanicus