1. Head without prominent eye lobe; single pair of eyes or eyes covering whole of head (may fade in alcohol)............... 2
- Head with distinct subtriangular eye lobe; two pairs of eyes present (may fade in alcohol)............................3
2. Eyes covering whole of head; Arctic Ocean, north-west Pacific Ocean, cold water species.............. Cyclocaris guilelmi
- Large eye not covering whole of head; Pacific Ocean species................................... Cyclocaris tahitensis
3. Pereopods 5–7 merus expansion broad, (L/W ratios 1.6, 1.7, 2.2 for P5–7 respectively) (see Figure 10: P5–7); Pereopod 6 basis with bevel; basis broadly expanded, subquadrate (see Figure 10:P6)................................. Cyclocaris franki
- Pereopods 5–7 merus expansion narrower, (L/W ratios 2.2, 2.8, 2.9 for P5–7) (see figure 6: P5–7); Pereopod 6 basis without bevel; basis expanded, oval (see Figure 6:P6)..................................................C yclocaris lowryi