Key to species of the genus Protolembos in the world (adult males)

1. Gnathopod 1, posterior margin of propodus heavily setose (> 100 setae)......................... P. ryukyuensis sp. nov.

- Gnathopod 1, posterior margin of propodus moderately or weakly setose (<ca. 50 setae)............................. 2

2. Gnathopod 1, anterior margin of propodus setose (ca. 25–50 setae).............................................. 3

- Gnathopod 1, anterior margin of propodus not setose......................................................... 4

3. Gnathopod 2 propodus wide (width/length = ca. 0.85).................................. P. drummondae Myers, 1988

- Gnathopod 2 propodus narrow (width/length <0.6).......................................................... 4

4. Gnathopod 1 palm with 1 rounded and 1 acute teeth......................................... P. arinyas Myers, 1988

- Gnathopod 1 palm with 1 angular and 1 acute teeth...................................... P. clematis (Moore, 1987)

5. Gnathopod 1, posterior margin of ischium heavily setose (> 25 setae)............................................ 6

- Gnathopod 1, posterior margin of ischium slightly or not setose (<5 setae)........................................ 8

6. Gnathopod 2 palm with a tooth....................................................... P. chiltoni (Myers, 1981)

- Gnathopod 2 palm lacking a tooth........................................................................ 7

7. Gnathopod 1 palm with 2 acute teeth.................................................. P. murrarum Myers, 1988

- Gnathopod 1 palm with 1 rounded and 1 acute teeth........................................ P. yaranus Myers, 1988

8. Gnathopod 1 palm with 2 acute teeth...................................................................... 9

- Gnathopod 1 palm with 1 angular and 1 acute teeth......................................................... 10

9. Gnathopod 2 palm with a tooth......................................................... P. kidoli (Myers, 1975)

- Gnathopod 2 palm lacking a tooth.................................................... P. crouyensis Myers, 1998

10. Sternal processes present, dactylus of gnathopod 1 almost straight.......................... P. tegulapodos Myers, 2002

- Sternal processes absent, dactylus of gnathopod 1 curved posteriorly.................... P. verrucularum (Moore, 1987)