Chaetostoma sacramento, Meza-Vargas & Ramirez & Lujan, 2024

Meza-Vargas, Vanessa, Ramirez, Jorge L. & Lujan, Nathan K., 2024, The ornate rubbernose pleco (Siluriformes, Loricariidae, Chaetostoma), a new species from the Ucayali River Basin, Peru, Zoosystematics and Evolution 100 (4), pp. 1387-1400 : 1387-1400

Chaetostoma sacramento sp. nov.

Fig. 2 , Tables 2 , 3

Chaetostoma sp. nov. Ucayali: Lujan et al. (2015 b) [molecular phylogeny].

Type material.

Holotype • Adult MUSM 72045 ; 65.1 mm SL; Peru, Ucayali Department, Padre Abad Province, Boqueron District, Shambillo, Amazon Basin, Ucayali River, unnamed left-bank tributary of Aguaytia River ; 09°0'29.88"S, 75°37'1.92"W; alt. 365 m; 07 Aug 2022; D. Faustino, J. Chuctaya, C. Nolasco, O. Quispe.

Paratype: All Peru, Amazon – Ucayali River Basin • MHNG 2712.042 , 1; 32.2 mm SL; tissues PE 08-122, 123, 124; Padre Abad Province, Aguaytia River at mouth of the Boca Yurac River ; 11 September 2008; S. Fisch- Muller, R. Covain, P. de Rham, H. Ortega, J. Figuerosa Minaya, J. Sanchez Ramirez • MUSM 71392 , 4; 50.5–79.4 mm SL; Pasco Department, Oxapampa Province, Palcazu District, Raya River ; 10°22'13.61"S, 75°7'52.90"W; 7 September 2022; R. Olivera, R. Quispe, J. Arana, M. Paniagua • MUSM 72046 , 34; 44.2– 12.5 mm SL; Ucayali Department, Padre Abad Province, Padre Abad District, Aguaytia River ; 9°4'8.58"S, 75°30'51.48"W; 8 August 2022; D. Faustino, J. Chuctaya, C. Nolasco, R. Quispe • ANSP 182805 , 3; 57.8–70.5 mm SL; same data as MUSM 71392 • ROM 114668 , 4; 54.3–76.7 mm SL; same data as MUSM 71392 .

Genseq- 2 COI.

GenBank accession number. Obtained from paratypes MUSM 72046 (OR 859576 and OR 859577) and MUSM 71392 (OR 859578 and OR 859579).

Genseq- 2 CytB.

GenBank accession number. Obtained from paratypes MUSM 72046 (OR 875871 and OR 875872).

Diagnosis.

Chaetostoma sacramento can be diagnosed from all congeners, except C. anomalum , C. branickii , C. dorsale , C. leucomelas , C. microps , C. nudirostre , C. palmeri and C. thomsoni by having distinct, white, variably-shaped spots or vermiculations ½ – 2 × nostril diameter on grey to brown background on the head (vs. spots absent or black on light-coloured background). Chaetostoma sacramento is distinguished from C. anomalum , C. branickii , C. dorsale , C. nudirostre and C. thomsonii by having highly variable, small to large distinct white spots, vermiculations or bands on the body (vs. spots, vermiculations or bands absent or black on light-coloured background), from C. anomalum by having adipose fin fully formed (vs. rudimentary), from C. dorsale by having uniformly brown adipose fin (vs. adipose fin with black spot), from C. leucomelas by having golden spots across the dorsal fin rays (vs. light bands), from C. microps by having eight branched dorsal-fin rays (vs. nine), from C. nudirostre by having curved cheek odontodes (vs. strait), from C. palmeri by having two predorsal plates (vs. three), excrescence present (vs. absent) and pelvic-fin insertion slightly posterior of dorsal-fin insertion (vs. pelvic-fin insertion at middle of dorsal-fin base).

Description.

Morphometric data in Table 2 and meristic data in Table 3 . Snout moderately depressed, dorsal profile of head convex from snout tip to dorsal-fin origin, then straight and gradually descending to adipose fin. Caudal peduncle dorsal profile slightly concave. Ventral profile straight from snout to caudal fin. Body depressed, deepest at dorsal-fin origin, shallowest at caudal peduncle; greatest width at pectoral girdle. Caudal peduncle slightly compressed, roundly triangular in cross-section.

Head wide, anteriorly rounded in dorsal view; snout anterior margin unplated, lacking odontodes and tentacles. Orbit small (5.2–6.6 % HL), dorsolaterally positioned, posterior margin aligned with vertical through anterior margin of cleithrum; skull roof flat. Oral disc wide, elliptical, occupying most of head width, lower lip ending just anterior to origin of opercular opening. Oval papillae covering upper lip, roundish papillae covering lower lip; all papillae smaller towards outer lip margins; lower lip margin crenulate. Buccal cavity with digitate papillae present posterior to premaxillary symphysis, one large patch of rugose papillae dorsomedial to each dentary tooth row. Maxillary barbel short (2.5–4.4 % HL). Premaxillary tooth row straight, joining contralateral tooth row at 160 º angle. Dentary straight, joining contralateral tooth row at 170 º angle. Teeth small, villiform, asymmetrically bicuspid. Opercle external border having row of six straight odontodes, odontodes slightly larger than elsewhere on body. Three to five type 3 hypertrophied hook-like evertible cheek odontodes (mode 5), odontodes hooked anteriorly, not reaching cleithrum. Supraoccipital excrescence restricted to vestigial longitudinal unplated patch, keel absent.

Flanks covered by five longitudinal plate series. Plates absent from abdomen and around dorsal-fin base. Body plates flat or gently curved, lacking keel or ridge. Dorsal-fin base bordered laterally by seven dorsal plates. Medial interdorsal plates five. Dorsal plate series with 20 plates, supramedian with 24, median series with 23, mid-ventral series with 24, ventral series with 19.

Dorsal fin II, 8; locking mechanism functional, spinelet V -shape, dorsal-fin origin slightly anterior to pelvic-fin origin, last dorsal-fin ray not reaching adipose fin when adpressed. Pectoral-fin rays I, 6; pectoral-fin spine reaching first third of pelvic fin when adpressed. Pelvic-fin rays i, 5; unbranched rays surpassing anal-fin origin; dorsal skin folds present on proximalmost two-thirds of unbranched pelvic-fin rays. Pectoral-fin spine with thicker odontodes irregularly distributed along entire dorsal, anterior and ventral surface of spine; one aligned row of larger odontodes along posterodorsal margin. Odontodes present on all, but posteriormost branched pectoral- and pelvic-fin rays. Anal-fin rays ii, 4, first unbranched ray almost as long as second. Second branched anal-fin ray longest, with remaining rays successively shorter. Caudal fin obliquely forked, lower lobe longer than upper; i, 7 + 7, i. Dorsal procurrent caudal-fin rays four, ventral two to four.

Colour in alcohol.

Head and body base colour brown dorsally, yellowish-white ventrally. Head with dense small white dots. In some specimens, scattered white spots on the body may be fused. Supraoccipital excrescence black or grey. Dorsal fin with white scattered spots on brownish base composed of melanophores distributed on rays and membrane. Remaining fins with brownish base composed of scattered melanophores. Tip of unbranched dorsal- and caudal-fin rays whitish in some individuals.

Sexual dimorphism.

Males with fleshy dorsal fold on the pelvic-fin leading ray. Males have more distinct, intense and contrasting white patterns on darker brown to black base colour. Females with duller colour patterns on lighter brown to black base colour.

Distribution.

Chaetostoma sacramento is known exclusively from the Pampa de Sacramento valley east of the eastern cordillera of the Andes in Peru, inhabiting the Negro River, a tributary of the Pisqui River in Loreto Department; the Yamino River, a tributary of the Aguaytia River; the Chui River, a tributary of upper San Alejandro River in Ucayali Department; and the Raya River, a left-bank tributary of Iscozacin River in Pasco Department (Fig. 1 ).

Etymology.

The species epithet sacramento refers to the plain (pampa) in central Peru between the Huallaga and Ucayali Rivers, approximately delimited by the Pisqui River in the north and Palcazu River in the south. Chaetostoma sacramento is currently known exclusively from this region, known as the Pampa de Sacramento, which occupies a valley between Huánuco and Ucayali provinces that is part of the Peruvian subandean belt and surrounds Boqueron del Padre Abad in the Cordillera Azul. The Pampa de Sacramento was first encountered by Europeans on 21 June 1726, by an expedition led by Don Juan Nunez Lobo and was christened Pampa del Sacramento to commemorate the Catholic ceremony of the Corpus Christi. Subsequent Franciscan missionaries highlighted the rich ethnic diversity of this region (IBC 2016). A noun in apposition.

Figures

Figure 1. Distribution of Chaetostoma sacramento type specimen sample sites along the Pampa del Sacramento in Andean left-bank tributaries of the Ucayali River Basin. Holotype (red star), green dots (paratypes), purple dots (aquarist trade).

Figure 2. Live holotype of Chaetostoma sacramento MUSM 72045, 65.1 cm, collected from the Yamino River, a tributary of the Aguaytía River. Photos by D. Faustino.