Hypoptopoma (Schaefer, 1991)

Aquino, Adriana E., 2010, Systematics Of The Genus Hypoptopoma Günther, 1868 (Siluriformes, Loricariidae), Bulletin of the American Museum of Natural History 2010 (336), pp. 1-110 : 22-23

Key to the species of Hypoptopoma

The following key has been designed for identification of fully developed individuals, which can be recognized by presence of a completely developed shield of abdominal plates.

1a. A single pair of slender plates posterior to coracoids, followed by series of 1–3 unpaired abdominal plates anterior to anal plate... 2

1b. Four to seven paired lateral abdominal plates posterior to coracoids; medial series of plates present or absent.................. 3

2a. Thoracic plates absent. Medial series of trunk lateral plates typically 20–22 (20).............................. H. spectabile (Upper Amazonas and upper Orinoco basins)

2b. Thoracic plates present. Medial series of trunk lateral plates typically 21–22 (21)........ H. sternoptychum (Upper and central Amazonas, including upper Madeira basin)

3a. Thoracic plates absent (fig. 9A). Second plate of midventral series of trunk plates contacting one plate of medial series only (fig. 8A). Four midventral plates between cleithral posterior process and first plate of ventral series or triangle-shaped plate above pelvic spine (fig. 8A)........................ 10

3b. Thoracic plates present (fig. 9B–C). Second plate of midventral series of trunk plates relating to two plates of medial series (fig. 8B). Three midventral plates between cleithral posterior process and first plate of ventral series or triangle-shaped plate above pelvic spine (fig. 8B)............... 4

4a. Anal shield composed of two plates—arranged along body longitudinal axis—between anus and abdominal plates (fig. 9C).......... H. bianale (Lower Ucayali and Solimões basins)

4b. Anal shield composed of azygous plate (fig. 9B)........................ 5

5a. Second infraorbital bone laterally contacting with one ventral dermal plate (fig. 5B). Distal tips of unbranched and branched rays of caudal fin dark forming vertical band along posterior margin of fin........ H. steindachneri (Lower Ucayali and Solimões basins)

5b. Second infraorbital bone laterally contacting with two ventral dermal plates (fig. 5A–C). Distal tips of unbranched and branched rays of caudal fin light, not forming vertical band along posterior margin of fin......... 6

6a. Patch of odontodes on anterolateral aspect of cleithrum present (at level of opening to branchial cavity)......... H. incognitum (Central Amazonas —including Madeira basin— Tocantins, and NE coastal rivers)

6b. Patch of odontodes on anterolateral aspect of cleithrum absent.................. 7

7a. No paranasal plate (fig. 7A).......... 8

7b. One or more paranasal plates (figs. 7B–C)... 9

8a. Odontodes on rostral margin of snout (rostral plate, first and second infraorbital) arranged in well-aligned dorsal and ventral series; both series separated by odontode-free discontinuity, particularly at level of first and second infraorbital bones (fig. 16). Medial series of trunk plates 20–22 (21)... H. inexspectatum (Ríos Paraguay and lower Paraná basins)

8b. Odontodes on rostral margin of snout typically not arranged in well-aligned dorsal and ventral series; if present, alignment restricted to rostral plate and series not separated by distinct odontode-free discontinuity. Medial series of trunk lateral plates typically 23... H. elongatum (Rios Tapajos and Trombetas)

9a. Dorsal fin with dark brown, roughly triangular spot, extended over base of anteriormost 3–4 branched rays, covering around one-third of first branched ray length. Anteriormost caudal-fin ‘‘,’’-shaped band connected at midpoint to lanceolate plates at base of fin (fig. 17D); upper arm of first band variably developed, typically light brown to absent......................... H. gulare (Lower Ucayali and Solimões basins)

9b. Dorsal fin without triangular spot at base of branched rays (if present, spot poorly defined). Anteriormost caudal-fin ‘‘,’’-shaped band not clearly connected at midpoint to lanceolate plates at base of fin (fig. 17G); upper-lobe arm of first band typically complete................ H. machadoi ( Rio Orinoco basin, including Rio Meta drainage)

10a. Preopercle with canal; pore of canal present, located between fourth infraorbital and canal-bearing plate (fig. 13B); both margin of canal-bearing plate and margin of fourth infraorbital bone with notch for exit of pore of canal in preopercle.............. 11

10b. Preopercle without canal, thus pore of canal between fourth infraorbital and canal-bearing plate absent (fig. 13A); both margin of canalbearing plate and fourth infraorbital smooth......................... 12

11a. Cleithral width 23.7 % –27.0 % of standard length (mean 25.7). Horizontal eye diameter 19.8 % –23.3 % of head length (mean 21.7). Caudal fin with diamond-shaped basal spot variably developed, followed by 2–3 faint vertical bands.................... H. brevirostratum (Tributaries of Rio Amazonas between confluence of Ucayali-Marañon)

11b. Cleithral width 19.1 % –23.5 % of standard length (mean 22.2). Horizontal eye diameter 13.6–20.7 of head length (mean 18.4). Caudal fin with variably shaped basal spot followed by 7–10 vertical bands...................... H. muzuspi (Rio Tocantins basin)

12a. Caudal fin with 7–10 brown vertical bands; dark spot along medial or lower-lobe branched rays absent. Adipose fin typically absent; if present, membranous................ H. baileyi (Upper Madeira basin)

12b. Caudal fin with 5 or fewer variably marked vertical bands; and dark spot along medial branched rays present, variably extended along lower-lobe rays. Adipose fin typically present, composed of bony axis and soft tissue.......................... 13

13a. Caudal fin with dark brown spot along medial branched rays slightly more extended over lower lobe, typically covering seventh ray on upper lobe and rays 8–11 on lower lobe (count starts dorsally) (fig. 17A). Cleithral width 20.0 % –24.7 % of standard length (mean 22.7).............. H. thoracatum (Amazonas basin, including Madeira, Purus, Tapajos, Caqueta, and lower Ucayali)

13b. Caudal fin with elongated dark spot along medial branched rays typically symmetrical, typically covering sixth and seventh rays of upper lobe and rays 8–9 of lower lobe (count starts dorsally) (fig. 17B–C). Cleithral width 17.3 % –21.4 % of standard length....... 14

14a. Caudal fin with elongated dark spot along medial branched rays connected to series of lanceolate plates at base of fin (fig. 17C). Head width 17.3 % –19.2 % of standard length (mean 18.4)..................... H. gu ia nen se ( Essequibo and Nickerie basins)

14b. Caudal fin with elongated dark spot along medial branched rays not distinctly connected to series of lanceolate plates at base of fin (fig. 17B). Head width 15.6 % –18.1 % of standard length (mean 17.1).......... H. psilogaster (Lower Ucayali and Napo basins)