Autapomorphies of Stethaprion erythrops:

1. Lateral coverage of dilator fossa by sixth infraorbital (69): (1> 0) almost complete, at least in its ventral border. Paralleled in Hyphessobrycon pulchripinnis .

2. Anterior extension of pelvic-bone along main axis (262): (0> 1) projecting anterior of lateral and medial lamellae of pelvic bone. Paralleled in the Gasteropelecidae, in node 302, and in Hoplias cf. malabaricus, Piabucus melanostomus, and Rhaphiodon vulpinus .

3. Number of dorsal pterygiophores (277): (0> 1) 11 or more. Paralleled in Stichonodon insignis .

4. Number of branched anal-fin rays (289): (0> 1) 35 or more. Paralleled in nodes 207 and 212 and in Gymnocorymbus ternetzi, Metynnis maculatus, Piabucus melanostomus, Pseudocorynopoma doriae, Rhaphiodon vulpinus, and Thoracocharax stellatus . Some trees: Paralleled in node 261 and in Markiana nigripinnis .

5. Pelvic-fin bony hooks in adult males of species bearing hooks on fins (309): (1> 0) absent. Paralleled in Creagrutus anary, Hyphessobrycon eques, H. luetkenii, Phenacogaster tegatus, and Pseudocorynopoma doriae . Some trees: Paralleled in Markiana nigripinnis and Psellogrammus kennedyi .

6. Semicircular grooves on posterior field of scales (323): (0> 1) present.