Key to species of Neoplecostomus

1a. Enlarged, fleshy folds between dentaries in all specimens, more evident in mature males ..................... N. doceensis

1b. Absence of the enlarged fleshy folds............................. 2

2a. Lateronasal plate absent ............................................... 3

2b. Lateronasal plate present, between nare and infraorbital 2 or posteriorly ........................................................... 10

3a. Adipose fin absent or poorly developed ....................... 4

3b. Adipose fin present and well developed ....................... 5

4a. Conspicuous dark spots all over the body; head depth 55.6-63.9% of head length ........................... N. botucatu

4b. Conspicuous dark spots all over the body absent; head depth 44.4-55.4% of head length ............. N. paranensis

5a. Moderate keels along each plate of lateral series, more evident in mature males; first plates in the mid-ventral series shorter than the area between them ..................... ............................................................. N. bandeirante

5b. Characters above absent ............................................... 6

6a. Mature males with enlarged odontodes and distinct swollen skin along lateral margins of snout ................. 7

6b. Mature males without enlarged odontodes and distinct swollen skin along lateral margins of snout ................. 8

7a. Ridge of swollen skin and enlarged odontodes in front of eyes in mature males; 17-24 teeth in premaxilla and 15-24 teeth in dentary ..................................... N. selenae

7b. Ridge of swollen skin and enlarged odontodes in front of eyes in mature males absent; 10-15 teeth in premaxilla and 8-12 teeth in dentary .................................... N. yapo

8a. Azygous preadipose plate present; cleithral width 19-23% of standard length; 5-13 teeth in dentary ............ N. microps

8b. Azygous preadipose plate absent; cleithral width 25-30% of standard length; 10-39 teeth in dentary .................... 9

9a. Orbital diameter 8.3-11.4% of head length; 7-9 plates between the adipose fin and caudal fin ......... N. langeanii

9b. Orbital diameter 12.2-13.0% of head length; 4-6 plates between the adipose fin and caudal fin ........ N. corumba

10a. Spinelet absent or weakly developed, usually narrower than dorsal-fin unbranched thick ray; canal plate divided in three smaller plates ................................ N. ribeirensis

10b. Spinelet present and always wider than dorsal-fin unbranched thick ray; canal plate simple, not divided......11

11a. Lateral-line plates 34-43; 10-13 plates between the adipose fin and caudal fin ............................ N. granosus

11b. Lateral-line plates 27-33; 4-9 plates between the adipose fin and caudal fin ........................................................ 12

12a. Head length 26.2-26.8% of SL; head width 96.7-97.0% of head length ............................................ N. variipictus

12b. Head length 28.0-34.5 of SL; head width 77.0-92.0% of head length ................................................................. 13

13a. Thoracic length 10.0-13.0% of SL ...... N. franciscoensis

13b. Thoracic length 13.2-17.6% of SL ........................... 14

14a. Premaxillary and dentary teeth more numerous in females than males, respectively 30-39 (vs. 14-20) and 30-38 (vs. 13-18); cleithral width 25.2-28.7% of SL; orbital diameter 9.5-11.4% of length of the head ........................ N. jaguari

14b. Premaxillary and dentary teeth number equivalent for males and females, respectively 15-35 and 19-38; cleithral width 19-21% of SL; orbital diameter 6-9% of head length ............................. N. espiritosantensis