Hypostomus lamberti, new species

(Figs. 1, 2 and 5a, Table 1)

urn:lsid:zoobank.org:act: AD125984-AEF3-4F7B-8B17-D02C2B8DAA54

Holotype. NUP 23640, 175.5 mm SL, Brazil, Goiás State, municipality of Niquelândia, Rio Bacalhau, tributary of Rio Bagagem, Rio Tocantins basin, -14.46531, -48.44662, 26 Mar 2019, G. Nardi, T. C Pessali, I. S. Penido & C. H. Zawadzki.

Paratypes. All from Brazil, Goiás State, municipality of Niquelândia, Rio Tocantins basin: MCP 15950, 8, 58.9–124.1 mm SL, Córrego Fundo, tributary of Rio do Peixe, -14.46666, -48.29999, 16 Jul 1992, R. E. Reis, J. Pezzi, E. H. L. Pereira & L. A. Porto. MZUSP 53988, 112, 23.5–89.5 mm SL, Córrego Água Parada, tributary of Rio do Peixe, -14.28333, -48.91666, 31 May 1996, M. T. Rodrigues. NUP 23641, 10, 67.5–125.0 mm SL; MCNIP 4967, 1, 116.5 mm SL; MNRJ 53854, 1, 89.2 mm SL; ZUEC 1770, 1, 87.0 mm SL, collected with holotype.

Diagnosis. Hypostomus lamberti is distinguished from the species of the H. cochliodon group by having bicuspid teeth with elliptic medial cusp and angle between dentaries usually larger than 80° (vs. spoon- or shovelshaped teeth and angle between dentaries about 80°). Hypostomus lamberti is diagnosed from the remaining congeners except H. affinis, H. ancistroides, H. argus, H. aspilogaster, H. borellii, H. boulengeri, H. carinatus, H. careopinnatus, H. coppenamensis, H. corantijni, H. cordovae, H. commersoni, H. crassicauda, H. delimai, H. dlouhyi, H. faveolus, H. formosae, H. gymnorhynchus, H. hemiurus, H. hoplonites, H. interruptus, H. krikati, H. micromaculatus, H. nematopterus, H. niceforoi, H. nigrolineatus, H. paucimaculatus, H. piratatu, H. punctatus, H. pusarum, H. rhantos, H. scabriceps, H. seminudus, H. spiniger, H. subcarinatus, H. tapijara, H. velhochico, H. watwata, and H. wilsoni by having moderate keels along the five lateral series of plates (vs. lacking keels); from H. coppenamensis, H. corantijni, H. crassicauda, H. gymnorhynchus, H. micromaculatus, H. nematopterus, H. paucimaculatus, and H. watwata by having roundish dark spots on head and flanks (vs. usually transverse ellipsoid dark spots on the body, see Weber et al. 2012); from remaining congeners, except H. commersoni, H. interruptus, H. rhantos and H. subcarinatus by having extremely small dark spots on head and anterior portion of trunk—more than 13 dark spots on the first plate in the dorsal series in specimens up to 82 mm SL (vs. less than 12 dark spots on the first plate in the dorsal series, medium to large spots on head and anterior portion of trunk); from H. commersoni by having moderate or blunt keels on lateral series of plates (vs. strong keels on lateral plates), by having short to moderate dorsal fin, far from reaching adipose plate (vs. long dorsal fin, from just to reaching adipose plate, see Garavello et al. 2012 and Cardoso et al. 2019); from H. interruptus by having anterior portion of trunk with similar color pattern to posterior portion in adults (vs. anterior portion of trunk with sharp spots and posterior portion with spots from inconspicuous to faded see Oyakawa et al. 2005); from H. rhantos by having lower caudal peduncle (8.1–9.8 % SL) (vs. deeper caudal peduncle 10.8–13.9 SL, see Armbruster et al. 2007), by having two parallel spot rows per inter-radial membranes in dorsal fin (vs. densely and unorganized spots per inter-radial membranes), by having spots diameter that increase in size posteriorly to head (vs. spots diameter not increasing in size); and from H. subcarinatus by having beige brown background coloration of dorsal fin, similar to the main body background in live specimens (vs. blue-tan dorsal fin), by having deeper head (18.2–20.7 % SL) (vs. 15.4–17.8 % SL see Zawadzki et al. 2019).

Description. Morphometric data are given in Table 1. Overall view of body in Figs. 1 and 2. Head moderately depressed and slightly compressed. Snout and anterior profile of head slightly pointed in dorsal view. Eye moderate in size (11.9–19.3% HL) dorsolaterally positioned. Greatest width of body at cleithrum, from this point, gradually narrowing to caudal-fin origin. Snout in lateral profile angled about 40° with ventral surface. Dorsal profile of head convex from tip of snout to vertical through interorbital region; slightly convex from that point to dorsal-fin origin; sloped downward to region just anterior dorsal procurrent caudal-fin rays and elevating again to caudal-fin insertion.

Ventral profile almost straight from snout tip to insertion of pelvic-fin unbranched ray; tapering slightly straight from pelvic-fin insertion to first ventral caudal-fin procurrent ray. Anterior portion of caudal peduncle rounded in cross-section; compressed on its posterior portion; slightly compressed on its dorsal region, flattened on ventral region. Mesethmoid forming weak longitudinal bulge from snout tip to nares. Supraoccipital bone with slightly developed median ridge and short posterior process bordered by single plate. Nasal raised. Conspicuous bulge originating lateral to nares, passing through supraorbital, and extending as ridge along dorsal portion of compoundpterotic. Opercle moderate in size, with small odontodes on its posterior border; its transversal length smaller to similar eye diameter. Oral disk round, moderate in size; its margins smooth. Lower lip short, far from transverse line through gill openings; ventral surface with two to three transverse dermal flaps posteriorly bordering each dentary ramus; short naked area proximally and larger area with numerous small papillae decreasing in size distally. Maxillary barbel moderately long, slightly larger than eye diameter; mostly free from lower lip. Odontodes present on anterior surface of upper lip, just below snout. Dentaries moderate to strongly angled, averaging from 90° to 100° between left and right dentary rami. Teeth bicuspid; medial cusp elliptic; lateral cusp smaller than medial cusp, except in some specimens that medial cusp of older teeth worn out to level of lateral cusp; crown bent inward. Internally to mouth, transversal areas of short papillae bordering each premaxillary and dentary teeth rami. Median buccal papilla present and well developed.

Trunk laterodorsally covered by five rows of dermal plates with moderately-developed odontodes, except on base of dorsal fin and small naked area on snout tip. Predorsal region with very slight median keel. Dorsal, middorsal, mid-ventral, and ventral series of plates with moderate keels. Median series with weakly developed keels; bearing uninterrupted lateral line. Ventral series bent ventrally. Ventral surface of head covered with platelets, except for region behind lower lip. Abdomen covered by minute platelets, with exception to very small areas around pectoral- and pelvic-fin insertions.

Dorsal fin II,7, first spine as spinelet; second spine flexible and slightly curved posteriorly; its origin at vertical just posterior midpoint between pectoral- and pelvic-fin insertions. Dorsal fin moderate in size; dorsal-fin spine slightly smaller than head length and similar to dorsal-fin base length; dorsal-fin distal border moderately convex; posteriorly not reaching adipose-fin spine. Adipose-fin spine compressed and almost straight. Pectoral fin I,6, its distal border straight. Pectoral-fin spine slightly curved backward, covered by poorly-developed odontodes; when adpressed reaching one-third pelvic-fin unbranched ray. Pelvic fin i,5, its distal border straight to slightly convex; when adpressed unbranched rays surpassing two to three plates beyond anal-fin origin. Anal fin i,4, distal tip reaching to sixth plate after its origin; distal margin convex. Caudal fin i,14,i; moderately falcate, unbranched rays longer than branched rays; ventral lobe slightly longer than dorsal.

Color in alcohol. Overall ground color grayish brown (Fig. 1). Head, dorsum, flanks and fins covered by numerous small dark spots except on lower lip. Spots extremely small, smaller than pupil diameter, numerous, close together and more conspicuous on head and on pre-dorsal region; increasing in length towards posterior region of body. From juveniles to adults spots become more numerous an close together on head and on pre-dorsal region. Spots on ventrolateral regions of trunk inconspicuous. Ventral surface of body with faded dark spots in some specimens. Spot diameters on dorsal fin greater than spots on body, forming two parallel spot rows per inter-radial membranes. Spot diameters on pectoral and pelvic fins greater than body spots, irregularly distributed on spine, membrane, and unbranched rays; sometimes spots in pelvic fin forming two parallel spot rows on membrane rays. Spot diameters on caudal fin greater than spots on body, inconspicuous.Ventral surface of body slightly clearer than dorsal surface.

Color in life. Similar to preserved specimens, except background color beige to brownish. Spots more conspicuous and visible on body (Fig. 2).

Distribution, habitat and conservation status. Hypostomus lamberti is known from only three localities, in the Rio Bacalhau, Córrego Fundo and Córrego da Água Parada, upper Rio Tocantins basin (Fig. 3). The Rio Bacalhau (type locality) in downtown of Niquelândia, have clear water, moderate flow, riparian vegetation fragmented, and substrate composed by sand, rocks, pebbles, and boulders (Fig. 4). Hypostomus lamberti is relatively abundant at type locality. The region surrounding the occurrence, as well as other locations in the upper Rio Tocantins basin, are far from being satisfactorily sampled. New records of the species are likely to be obtained with increasing sampling efforts in the region. The drainages that the species occurs have been impacted by anthropogenic activities like deforestation, siltation, contamination by domestic sewage, cattle ranching, mining, and construction of reservoirs. However, no specific threats were detected, and Hypostomus lamberti is provisionally classified as Least Concern (LC) in the IUCN criteria (IUCN Standards and Petitions Subcommittee, 2022) (IUCN, 2022).

Etymology. The specific epithet lamberti is in honor to Brazilian ichthyologist Mauro César Lambert de Brito Ribeiro (Instituto Brasileiro de Geografia e Estatística—IBGE), in recognition to his contributions to knowledge of the diversity and distribution of ichthyofauna in the central plateau of Brazil. A noun in the genitive case.

Remarks. Ontogenetic variation in morphometric measurements and color pattern was detected in Hypostomus lamberti. The proportion of the head length and cleithral width of the holotype are smaller than the range of the proportion of these measurements in the paratypes, while the caudal peduncle length is larger (Table 1). There is a great size discontinuity between the holotype and the paratypes, with the holotype being 50 mm larger (175.5 mm SL) than the larger paratype (125.0 mm SL) which resulted in a negative allometry (Fig. 6).

A distinctive feature of Hypostomus lamberti is its color pattern, which distinguishes it from most congeners. However, this color pattern also undergoes changes during ontogenetic development. In smaller specimens, up to 82 mm SL, the spot pattern on head is more inconspicuous and spaced apart. As specimens grow, the spot pattern becomes more prominent, and the spots come closer together.