Autapomorphies of Hyphessobrycon socolofi:

1. Relative size of frontal and parietal fontanels (23): (1> 0) length of frontal fontanel up to 2/3 length of parietal fontanel. Some trees: Paralleled in Hyphessobrycon elachys .

2. Number of gill rakers on first hypobranchial and ceratobranchial (195): (1> 0) 16 or more. Paralleled in nodes 177 and 183 and in Astyanax latens, A. cf. rutilus, A. pelegrini, Hoplias cf. malabaricus, Moenkhausia dichroura, Parecbasis cyclolepis, Piaractus mesopotamicus, and Stichonodon insignis .

3. Pectoral-fin bony hooks in adult males of species bearing hooks on fins (310): (0> 1) present. Paralleled in node 268 and in Astyanax cf. asuncionensis, A. lineatus, Bario steindachneri, Bryconamericus cf. iheringii, B. rubropictus, Hyphessobrycon luetkenii, and Phenacogaster tegatus .

4. Dorsal-fin bony hooks in adult males of species bearing hooks on fins (311): (0> 1) present. Paralleled in nodes 248 and 268 and in Astyanax cf. asuncionensis, A. lineatus, Bario steindachneri, Bryconamericus rubropictus, Hyphessobrycon luetkenii, Nematocharax venustus, and Probolodus heterostomus .

5. Caudal-fin bony hooks in adult males of species bearing hooks on fins (312): (0> 1) present. Paralleled in node 268 and in Acrobrycon tarijae, Astyanax cf. asuncionensis, A. lineatus, Bario steindachneri, Hyphessobrycon luetkenii, and Probolodus heterostomus .