| 1a | - Median row of abdominal scutes incomplete; 2-5 anterior scutes present
| 2 |
| 1b | - Median row of abdominal scutes absent or complete; 0-1 anterior median scutes present
| 4 |
| 2a | - Breeding odontodes on side of head long, second row of anterior lateral scutes thickened and forming a smoothly keeled ridge
| 9 |
| 2b | - Breeding odontodes on side of head short, second row of anterior lateral scutes flat and smoothly keeled ridge absent
| 3 |
| 3a | - Snout-mouth length/pectoral fin length larger than 1.0
| |
| 3b | - Snout-mouth length/pectoral fin length smaller than 0.6
| |
| 4a | - Three rows of abdominal scutes
| 5 |
| 4b | - Two rows of abdominal scutes
| 21 |
| 5a | - Four rows of anterior lateral scutes, all rows complete
| 6 |
| 5b | - Five rows of anterior lateral scutes, middle row may be complete or incomplete
| 15 |
| 6a | - Snout-mouth/head length less than 0.5
| 7 |
| 6b | - Snout-mouth/head length equal or more than 0.5
| 12 |
| 7a | - Outer rays (except outermost ray) of lower caudal fin lobe darkly pigmented to base; breeding male with head and snout almost totally covered with breeding odontodes
| 8 |
| 7b | - Outer rays (except outermost ray) of lower caudal fin lobe pigmented only at distal end; breeding male with head and snout not almost totally covered with breeding odontodes
| 10 |
| 8a | - Male with small breeding odontodes on head and snout; snout dairly long and narrow
| |
| 8b | - Male with long breeding odontodes on sides of head; snout short and broad
| 9 |
| 9a | - In adult male, with body depth less than snout-mouth length
| |
| 9a | - In adult male, body depth greater than snout-mouth length
| |
| 10a | - Scutes of head and snout lack very dark reticulations
| |
| 10b | - Scutes of head and snout with very dark reticulations
| 11 |
| 11a | - Caudal fin with distinct clear ocellus bar in dark stripes
| |
| 11b | - Caudal fin lacks distinct clear ocellus bar in dark stripes
| |
| 12a | - Head and snout of breeding male densely covered with breeding odontodes; males mature at small size (below 100mm); lower body of cleithrum narrow; snout narrow
| |
| 12b | - Head and snout of breeding male sparsely covered with breeding odontodes; males mature at large size (more than 125mm); lower body of cleithrum broad; snout broad
| 13 |
| 13a | - Anterior body scutes diamond in shape; caudal peduncle narrow, last few dorsal scutes longer than wide; no breeding odontodes on preorbital ridge
| |
| 13b | - Anterior body scutes hexagonal in shape; caudal peduncle broad, last few dorsal scutes wider than long; breeding odontodes on preorbital ridge
| 14 |
| 14a | - Species coming from Amazon river system
| |
| 14b | - Species coming from Paraná river system
| |
| 15a | - Snout-mouth length/head length less than 0.5
| |
| 15b | - Snout-mouth length/head length equal or more than 0.5
| 16 |
| 16a | - Body depth/pelvic fin length equal or more than 0.86
| |
| 16b | - Body depth/pelvic fin length less than 0.86
| 17 |
| 17a | - Pectoral fin length/snout-mouth length less than 0.62
| |
| 17b | - Pectoral fin length/snout-mouth length more than 0.65
| 18 |
| 18a | - Breeding odontodes not greatly enlarged on lateral scutes; on some individuals first anal and dorsal rays entirely darkly pigmented, other dorsal and anal rays not entirely pigmented
| |
| 18b | - Large breeding odontodes on lateral scutes; first anal and dorsal rays never more darkly pigmented than other dorsal and anal rays
| 19 |
| 19a | - Snout-mouth length/pectoral fin length more than 1.25; pectoral and pelvic fin rays and spines uniformly pigmented, without distinct dark spots
| |
| 19b | - Snout-mouth length/pectoral fin length equal or less than 1.0; pectoral fins rays and spines with distinct spots
| 20 |
| 20a | - Body depth/pectoral fin length equal or less than 0.41; 24 post-anal plates
| |
| 20b | - Body depth/pectoral fin length more than 0.44; 22-23 post-anal plates
| |
| 21a | - Median abdominal scute at base of pelvic fins
| 22 |
| 21b | - No median abdominal scute at base of pelvic fins
| 25 |
| 22a | - In adult, lower body of ceithrum narrow, may be in two parts; preorbital ridge and eye elevated over head
| |
| 22b | - In adult, lower body of cleithrum broad or very broad; only eye elevated over head
| 23 |
| 23a | - Body of cleithrum very broad
| |
| 23b | | 24 |
| 24a | - In adult snout-mouth length less then 3.0 times interorbotal with; 2-3 median abdominal scutes at anterior of abdomen
| |
| 24b | - In adult, snout-mouth length more than 3.3 times interorbital width; usually 1 median abdominal scute at anterior of the abdomen
| |
| 25a | - Snout-mouth length/interorbotal width equal or less than 1.8 in adult male; outer rays (except outermost ray) of lower caudal fin lobe usually not entirely darkly pigmented from fin base to tip
| 26 |
| 25b | - Snout-mouth length/ interorbital width more than 1.9 in adult male; outer rays (except outermost ray) of lower caudal fin lobe darkly pigmented from fin base to tip but may be interrupted by clear ocellus bar
| |
| 26a | - Pectoral fin does not reach pelvic fin origin; mid-dorsal ridge of head absent in adults
| |
| 26b | - Pectoral fin reaches or extends past pelvic fin origin; mid-dorsal ridge present in adults
| 27 |
| 27a | - Head covered by medium-sized breeding odontodes
| |
| 27b | - Head not covered by medium-sized breeding odontodes; small breeding odontodes on preorbital ridge only or absent
| 28 |
| 28a | - Interradial membranes of caudal fin clear; many small breeding odontodes on preorbital ridge
| |
| 28b | - Interradial membranes of caudal fin darkly pigmented; few, if any, very small breeding odontodes on preorbital ridge
| |
