Key to Australian species of Gastroptychus

1. Anterior margin of sternite 3 concave, with row of spines. Third maxillipeds widely separated......................... 2

- Anterior margin of sternite 3 with median ridge anteriorly produced and sloping down in ventral view. Third maxillipeds close to each other........................................................................................ 3

2. Pereopods 2–4 propodi much shorter than carpi (length at most 1/7 that of carpi).............. G. brachyterus Baba, 2005

- Pereopods 2–4 propodi much longer than carpi................................... G. sternoornatus (Van Dam, 1933)

3. Abdomen totally covered with spines..................................................... G. ro ge ri Baba, 2000

- Abdomen partly covered with spines..................................................................... 4

4. Abdominal somite 3 with low processes on pleura, without spines........... G. investigatoris (Alcock & Anderson, 1899)

- Abdominal somite 3 with small spines on pleura.......................... G. hendersoni (Alcock & Anderson, 1899)