Key to the species of the genus Ione (based on females).

1. Pereomeres 1–4 with lateral plates subdivided (appearing segmented)............................................ 2

– Pereomeres with lateral plates not subdivided............................................................... 3

2. Pereomeres with lateral plates thick.............................................................. I. thompsoni

– Pereomeres with lateral plates thin........................................................... I. sarahae n. sp.

3. Coxal plates 1–6 greatly enlarged........................................................................ 4

– Coxal plates 1–6 not enlarged........................................................................... 5

4. Pleomeres and lateral plates with numerous filiform extensions.......................................... I. tubulata

– Pleomeres and lateral plates with few filiform extensions............................................ I. taiwanensis

5. Pereon ovate, length subequal to width................................................................ I. ovata

– Pereon elongate, longer than wide........................................................................ 6

6. Coxal plates 1 and 2 enlarged, asymmetrical....................................................... I. thoracica

– Coxal plates 1 and 2 not enlarged, symmetrical....................................................... I. cornuta