Hypostomus, Lacepede, 1803

Key to the species of Hypostomus View in CoL from the Brazilian portion of the rio Paraguai basin (adapted from Tencatt, 2022)

1a. Exposed portion of opercle, when present, completely bordered by a thick layer of skin ................................................................................2

1b. Exposed portion of opercle bordered by bony plates ............................................... 4

2a. Dark spots absent on the body.................................................................... H. basilisko View in CoL

2b. Dark spots present on the body .................................................................................. 3

3a. Seven to nine teeth in each mandibular ramus; spoon-shaped medial cusp........................................................................ H. cochliodon View in CoL

3b. 8 to 44 teeth on each mandibular ramus; medial cusp typically spatulate/shovel shaped; variably villiform ........................................................................... H. khimaera View in CoL

4a. Head and trunk with pale spots and/or transverse and/or diagonal pale bars ..........5

4b. Head and trunk with dark spots; spots variably diffuse or absent ............................. 6

5a. Posterior half of flanks with transverse pale bars ........................................................ H. peckoltoides View in CoL (*and juveniles of H. latifrons View in CoL )

5b. Posterior half of flanks lacking transversal pale bars ...................................... H. regani View in CoL

6a. Adipose fin absent ............................................................................... H. careopinnatus View in CoL

6b. Adipose fin present ......................................................................................................7

7a. Unicuspid teeth ............................................................................................. H. perdido View in CoL

7b. Bicuspid teeth .............................................................................................................. 8

8a. Markedly wide body (dorsal view); unbranched caudal-fin rays conspicuously elongated, with size similar to predorsal length.......................................... H. ternetzi View in CoL

8b. Clearly narrower body (dorsal view); unbranched caudal-fin rays slightly to moderately elongated, with size similar to head length ............................................ 9

9a. Three predorsal plates bordering the supraoccipital bone.......................... H. latifrons View in CoL

9b. One predorsal plate bordering the supraoccipital bone...........................................10

10a. Triangular snout in dorsal view; short dentaries; mid-dorsal series of bony plates with keels varying from moderately to well-developed .............. H. boulengeri View in CoL

10b. Rounded snout in dorsal view; dentaries varying from moderate to long in size; mid-dorsal series of bony plates with keels, when present, poorly developed .....11

11a. Body densely covered with relatively small and closely spaced spots; dorsal and mid-dorsal series of lateral bony plates with moderately hypertrophied odontodes ........................................................................... H. renestoi

11b. Body covered with relatively large and more spaced spots; dorsal and mid-dorsal series of lateral bony plates devoid of hypertrophied odontodes................ 12

12a. Mandibular ramus with 10 to 61 teeth ...................................................................13

12b. Mandibular ramus with 68 to 111 teeth .................................................................14

13a. Blotches on head closely-spaced and relatively numerous; distance between adjacent blotches conspicuously smaller than diameter of blotches....... H. froehlichi

13b. Blotches on head more distant from each other and relatively fewer; distance between adjacent blotches similar to their diameter...................... H. fuscomaculatus

14a. Head moderately compressed, with two parallel keels in the pre-dorsal region .................................................................. H. latirostris View in CoL

14b. Head moderately depressed, lacking conspicuous keels in the pre-dorsal region ................................................................... H. mutucae View in CoL

*Juvenile and adult individuals of H. peckoltoides Zawadzki, Weber & Pavanelli, 2010 View in CoL can be distinguished from juveniles of H. latifrons Weber, 1986 View in CoL by having only one predorsal plate bordering the supraoccipital bone (vs. three plates).