Pseudancistrus zawadzkii Silva, Roxo, Britzke & Oliveira 2014

Pseudancistrus zawadzkii can be distinguished from all known congeners, except members of the P. barbatus group, by the possession of hypertrophied odontodes along the snout margin and the absence of evertible cheek plates. It further differs from other congeners by the combination of the following characters: whitish spots that abruptly increase in size between the head (diameter 1.1-1.3 mm) and body (diameter 2.6-3.0 mm); odontodes along margin of snout increasing gradually in length from posterior of snout tip to cheek; longest odontodes on posterior most portion of non-evertible cheek plates.; rounded spots that do not cover more than one plate along the body; head depth 67.0-72.7% of HL; cleithral width 35.2-38.0% of SL; distance between posteromedial margin of supraoccipital and dorsal-fin origin 6.7-9.2% of SL; anal-fin spine length 11.9-13.8% of SL; peduncle depth 12.5-14.2% of SL; and internares distance 12.7-16.6% of HL (Ref. 95679).

Dorsal spines (total): 2; Dorsal soft rays (total): 7; Analspines: 1; Analsoft rays: 5

Inhabits clear water rivers, varying from medium to large size, with rocky outcrops formingsmall waterfalls and substrates of rocks and sand (Ref. 95679).

Distribution of several Pseudancistrus species, with P. zawadzkii shown in red.

Pseudancistrus zawadzkii is a species of catfish in the family Loricariidae. It is native to South America, where it occurs in the Tapajós basin, including the Tracuá River, in Brazil. It is typically found in areas with clear water, rocky outcrops, small waterfalls, and a substrate of rocks and sand. The species reaches 12.9 cm (5.1 inches) SL.

P. zawadzkii was described in 2014 by Gabriel S. C. Silva, Fábio F. Roxo, and Claudio Oliveira (all of São Paulo State University), as well as Ricardo Britzke (of the National University of San Marcos). Its specific epithet, zawadzkii, refers to Cláudio Henrique Zawadzki, a professor at the State University of Maringá, honoring his contributions to the study of Loricariidae.

P. zawadzkii sometimes appears in the aquarium trade, where it is typically known either as the Tapajós stream pleco or by its associated L-number, which is L-321.

Morphometric data presented in Table 1. In lateral view, dorsal profile convex from snout tip to dorsal-fin origin; straight, gradually descending from dorsal-fin origin to posterior insertion of adipose fin; straight, steeply ascending to insertion of caudal fin; ventral profile flat from snout tip to anal-fin origin; shallowly concave from anal-fin insertion to lower caudal-fin spine; greatest body depth at dorsal-fin origin. In dorsal view, greatest body width across cleithral region; snout broadly elliptical; body progressively narrowed from opercular region to caudal fin. Cross-section of body between pectoral and pelvic fins rounded dorsally and flattened ventrally; cross-section of caudal peduncle ellipsoid. Morphometric data for Pseudancistrus zawadzkii. Pseudancistrus zawadzkii n = 5 Holotype Range Mean SD Standard length (SL) 116.4 128.7−87.5 109.5 Percents of SL Predorsal length 43.3 43.1−46.1 44.5 1.3 Head length 36.6 32.9−37.8 36.3 1.9 Head-dorsal length 6.7 6.7−9.2 8.1 1.2 Cleithral width 35.2 35.2−38.0 36.7 1.2 Head pectoral length 30.5 29.6−32.2 30.9 0.9 Thorax length 23.5 21.2−23.5 22.5 1.1 Pectoral-spine length 31.5 31.3−33.2 31.9 0.7 Abdominal length 24.2 22.6−26.1 24.3 1.3 Pelvic-spine length 28.4 25.6−28.4 27.2 1.2 Post-anal length 31.2 29.6−31.2 30.5 0.7 Anal-fin spine length 12.5 11.9−13.8 12.6 0.7 Dorsal pectoral depth 27.3 26.6−30.7 28.6 1.7 Dorsal spine length 24.7 24.7−29.9 27.5 2.3 Dorsal pelvic depth 22.9 22.1−26.4 24.1 1.7 Dorsal-fin base length 31.2 29.1−31.2 30.0 1.0 Dorsal-adipose distance 11.2 10.5−13.7 11.6 1.2 Adipose-spine length 7.8 6.79−8.78 7.8 0.7 Dorsal adipose caudal distance 11.7 11.7−15.6 13.7 1.7 Caudal peduncle depth 12.5 12.5−14.2 13.3 0.6 Ventral adipose caudal distance 22.9 22.9−25.3 23.9 1.0 Adipose anal distance 21.3 18.5−21.3 19.8 1.0 Dorsal-anal distance 16.0 15.8−17.8 16.8 0.8 Pelvic-dorsal distance 29.5 22.0−29.5 22.5 2.7 Percents of head length (HL) Head-eye length 29.4 28.1−30.1 29.1 0.8 Orbital diameter 14.6 14.5−18.8 15.8 1.7 Snout length 63.2 63.2−70.5 66.8 3.1 Internares width 14.4 12.7−16.6 14.4 1.4 Minimal interorbital distance 28.8 28.8−35.7 32.2 2.5 Mouth length 53.8 52.0−60.6 55.7 3.5 Barbel length 14.0 7.6−14.0 10.6 2.6 Dentary tooth cup length 17.6 17.0−19.6 18.5 1.1 Premaxillary tooth cup length 17.8 17.2−19.2 18.2 0.7 Head depth 68.9 67.0−72.7 68.8 2.3 Body almost entirely covered by plates; ventral portions of head and abdomen and dorsal-fin base naked. Five lateral rows of dermal plates, dorsal plates 21−24, lateral mid-dorsal plates 19−21, lateral median plates 22−24, lateral mid-ventral plates 21−24, lateral ventral plates 18−20. Three predorsal plates; eight plates below dorsal-fin base; four plates between dorsal fin and adipose fin; five rows of plates on caudal peduncle. Dorsal spinelet present. Body plates and cleithrum have minute odontodes. Odontodes slightly hypertrophied on pectoral-fin spines, becoming gradually larger towards tips. Numerous yellowish hypertrophied odontodes along lateral margins of head including snout; odontodes small on tip of snout, increasing gradually in length from anterolateral margin of snout to cheeks; longest odontodes on posterior most portion of non-evertible cheek plates. Eyes small (orbital diameter 14.5−18.8% of HL), dorsolaterally positioned. Oral disk transversely ellipsoid. Lower lip not reaching transverse line between gill openings. Lower lip covered with numerous small papillae. Maxillary barbel developed. Mouth relatively large. Premaxillary teeth 40−61 per ramus; dentary teeth 28−69 per ramus. Teeth bifid, medial cusp large and rounded, lateral cusp minute and pointed. Wide jaws, dentary bones forming an oblique angle, premaxillary bones almost co-linear. Dorsal fin II,7, origin approximately at midpoint between pectoral- and pelvic-fin origins, last dorsal-fin ray reaching adipose fin when depressed. Pectoral fin I,6, spine tip curved inward, covered with enlarged odontodes distally; depressed tip reaching one-third length of pelvic-fin spine. Pelvic fin I,5, spine tip curved inward, almost reaching anal-fin origin when depressed. Anal fin I,5, spine tip straight, reaching seventh plate posterior to its origin. Caudal fin I,7−I,7, distal margin concave, inferior lobe longer than superior. Adipose fin with lightly curved spine, preceded by single median preadipose plate.

Pseudancistrus zawadzkii is known from rio Tapajós (04°33'10"S, 56°18'W) and rio Tracuá (04°28'11"S, 56°17'01"W), municipality of Itaituba, all from rio Tapajós basin, Pará State, Brazil. (see Fig. 4 for distribution map of type species localities).