| 1. | Eyes present | 2 |
| Eyes absent | 4 | |
| 2. | Pereonites 6 and 7 bearing strong lateral protrusions | R. aculeata (Lepechin, 1780) |
| Pereonites 6 and 7 laterally smooth | 3 | |
| 3. | Telson minutely cleft, coxa 1 slightly elongated | R. natator (Holmes, 1808) |
| Telson cleft half its length, coxa 1 drawn out width of head | R. macropus Sars, 1893 | |
| 4. | Head with strong dorsal protrusion | R. marinae Lörz, Jażdżewska & Brandt, 2018 |
| Head dorsally smooth | 5 | |
| 5. | Rostrum extending beyond acute anterior head lobe | 6 |
| Rostrum short, third epimeral plate smooth | R. saskia n. sp. | |
| 6. | Third epimeral plate strongly serrate, telson incised 20% | R. flemmingi Dahl, 1959 |
| Third epimeral plate weakly serrate, telson cleft 10% | R. distincta (Holmes, 1908) |
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