Key to species of Austinixa

1. Carapace without branchial ridges........................................................................ 2

- Carapace with branchial ridges.......................................................................... 5

2. P4 propodus opposable margin bicarinate.................................................................. 3

- P4 propodus opposable margin with single carina (NE FL, GMx, Car)............... A. gorei (Manning & Felder, 1989)

3. Male carapace with patch of short setae on posterior third, just anterior to cardiac ridge. Male pleon telson subtriangular or semicircular, not wider than long......................................................................... 4

- Male carapace without patch of short setae on posterior third, just anterior to cardiac ridge. Male pleon telson semiellipsoid, clearly wider than long. (E Pac)................................................... A. felipensis (Glassell, 1935)

4. Male pleon telson subtriangular. Setal patch on male carapace posterior third connecting with setae on lateral regions. Female carapace with setae on lateral regions extending also onto anterolateral regions. (E Pac)............... A. cuestai sp. nov.

- Male pleon telson semicircular. Setal patch on male carapace posterior third clearly separated from setae on lateral regions. Setae on female carapace confined to most lateral regions (SW Atl)............................ A. aidae (Righi, 1967)

5. Branchial ridges each extending to orbits (SW Atl)................................ A. patagoniensis (Rathbun, 1918)

- Branchial ridges falling short of orbits..................................................................... 6

6. P4 merus with distinct depression on posterior or dorsal surface................................................ 7

- P4 merus without distinct depression on posterior or dorsal surface.............................................. 8

7. P4 merus with proximal depression on posterior to posterodorsal surface into which dactylus of P5 fits. (SW Atl)........ A. leptodactyla (Coelho, 1997)

- P4 merus with pubescent distal depression on dorsal surface, not positioned to fit P5 dactylus (Car)...... A. roblesi sp. nov.

8. Male carapace without patch of short setae on posterior third, just anterior to cardiac ridge........................... 9

- Male carapace with patch of short dark setae on posterior third, just anterior to cardiac ridge. (SW Atl)............................................................................................... A. bragantina Coelho, 2005

9. Branchial ridges angled laterally, with sharp bend toward posterior............................................. 10

- Branchial ridges extending laterally or gently curved towards posterior lacking sharp bend laterally................... 11

10. P4 propodus opposable margin with single carina. First gonopod with truncate apex (GMx)........ A. chacei (Wass, 1955)

- P4 propodus opposable margin bicarinate. First gonopod apex hooked, styliform (GMx)................................................................................................... A. behreae (Manning & Felder, 1989)

11. P5 dactylus clearly reaching beyond distal end of P4 merus. P4 merus anterior margin carinate, carina not clearly laminate. Carapace depressions lateral to front narrow and short, not reaching dorsally to near branchial ridges. Carapace 2.2–2.9 times wider than long. Male telson semicircular (NW Atl, GMx)............................... A. cristata (Rathbun, 1900)

- P5 dactylus not clearly reaching beyond distal end of P4 merus. P4 merus anterior margin flattened into strongly laminate crest; merus posterior half robust, clearly swollen. Carapace depressions lateral to front reaching nearly to branchial ridges. Carapace 1.7–2.3 times wider than long. Male telson prolate semiellipsoid, less than twice as wide as long (Car)...................................................................................................... A. artankeri sp. nov.