Ancistrus, Kner, 1854

Key to the species of Ancistrus View in CoL without an adipose fin.

1. Snout usually without tentacles in adults; two or more plates of the dorsal plate series between end of postdorsal ridge and origin of first dorsal procurrent caudal-fin spine ( Fig. 4a View Fig ) ................................................................................. 2

1’. Snout with tentacles in adults; one or no plate of the dorsal plate series between end of postdorsal ridge and origin of first dorsal procurrent caudal-fin spine ( Fig. 4b View Fig ) .............. 3

2. Body narrow (27.5-31.2% SL at cleithrum) and depressed (15.6-16.9% SL at supraoccipital); with preanal plateletlike element ......... A. tombador View in CoL (upper rio Tapajós basin)

2’. Body wide (31.4-33.1% SL at cleithrum) and deep (17.9- 19.3% SL at supraoccipital); without preanal platelet-like element ............. A. verecundus View in CoL (upper rio Madeira basin)

3. Length of mandibular tooth row 19.4-24.0% HL; caudalpeduncle depth 9.6-10.7% SL; teeth on dentary 62-80 and premaxilla 61-78 ................................................................... 4

3’. Length of mandibular tooth row 14.8-17.0% HL; caudalpeduncle depth 8.5-9.4% SL; teeth on dentary 50-59 and on premaxilla 47-55 ... A. parecis View in CoL (upper rio Tapajós basin)

4. Predorsal length 43.8-46.4% SL; occipital depth 14.9-17.0% SL; caudal peduncle length 27.7-30.9% SL ....................... ..................................... A. reisi View in CoL (upper rio Tocantins basin)

4’. Predorsal length 47.5-49.3% SL; occipital depth 17.0-19.5% SL; caudal peduncle length 24.6-27.1% SL ....................... ........................... A. jataiensis View in CoL (upper rio Tocantins basin)