Hisonotus alberti, Roxo, Fábio F., Silva, Gabriel S. C., Waltz, Brandon T. & Melo, Jorge E. G., 2016

Roxo, Fábio F., Silva, Gabriel S. C., Waltz, Brandon T. & Melo, Jorge E. G., 2016, A new species of Hisonotus (Siluriformes: Otothyrinae) from the upper rio Paraná and rio São Francisco basins, Brazil, Zootaxa 4109 (2), pp. 227-238 : 228-234

Hisonotus alberti n. sp.

( Figs. 1–4 , Table 1)

Holotype. MZUSP 118845 (male, 33.5 mm SL), Brazil, Minas Gerais State, municipality of São Roque de Minas, ribeirão das Posses, upper rio Paraná basin, 20°17'15"S, 46°34'53"W, 19 May 2011, col. J.A. Senhorini, P.S. Cecarelli, J. O. Junqueira, R. Devidé, R. Rocha, M.N. Mehanna.

Paratypes. All from Minas Gerais State, Brazil (67 specimens). ANSP 200148, (2 females, 32.1–34.0 mm SL, 2 males, 29.8–31.7 mm SL), municipality of São Roque de Minas, ribeirão das Posses, upper rio Paraná basin, 20°14'54"S, 46°38'24"W, 10 April 2010, col. J.A. Senhorini, P.S. Cecarelli, J. O. Junqueira, R. Devidé, R. Rocha, M.N. Mehanna. LBP 10245 (6 males, 28.9–30.5 mm SL), municipality of São Roque de Minas, córrego Luciano, rio São Francisco basin, 20°18'44"S, 46°31'51"W, 0 8 April 2010, col. J. O. Junqueira, R. Devidé, R. Rocha, M.N. Mehanna. LBP 10266 (9 females, 25.6–34.9 mm SL, 11 males, 28.5–31.8 mm SL, 7 C&S, sex and measurements not determined), municipality of São Roque de Minas, ribeirão das Posses, upper rio Paraná basin, 20°14'54"S, 46°38'24"W, 10 April 2010, col. J.A. Senhorini, P.S. Cecarelli, J. O. Junqueira, R. Devidé, R. Rocha, M.N. Mehanna. LBP 11847 (2 females, 24.3–33.4 mm SL, 2 males, 30.4– 30.3 mm SL) collected with holotype. LBP 17388 (6 females, 24.9–33.4 mm SL, 2 males, 29.3–30.1 mm SL), municipality of Oliveira, córrego Caxambú, upper rio Paraná basin, 20°47'52"S, 44°52'35"W, 19 February 2013, col. R. Devidé, G.S.C. Silva, C. Araya, V.F. Sene. MPUJ 8199, (2 females, 27.6–31.4 mm SL, 4 males, 28.5–30.5 mm SL), municipality of São Roque de Minas, ribeirão das Posses, upper rio Paraná basin, 20°14'54"S, 46°38'24"W, 10 April 2010, col. J.A. Senhorini, P.S. Cecarelli, J. O. Junqueira, R. Devidé, R. Rocha, M.N. Mehanna. NUP 9437 (2 females, 25.9–32.4 mm SL), municipality of Oliveira, córrego Caxambú, upper rio Paraná basin, 20°48'06"S, 44°52'41"W, 23 July 2009, col. F. Correa. NUP 9440 (3 females, 32.7–34.6 mm SL, 2 males, 30.2–31.9 mm SL), municipality of Oliveira, córrego Caxambú, upper rio Paraná basin, 20°48'06"S, 44°52'41"W, 14 January 2009, col. F. Correa. NUP 9441 (4 males, 27.4–30.0 mm, 1 C&S, sex and measurements not determined), municipality of Oliveira, córrego Caxambú, upper rio Paraná basin, 20°48'06"S, 44°52'41"W, 14 January 2009, col. F. Correa.

Diagnosis. The new species can be distinguished from all congeners by possessing an exposed abdomen (i.e., area bounded by cleithral region and urogenital opening) with no dermal plate development ( Fig. 2 a) and with the exception of extremely small platelets present near urogenital opening in some specimens ( Fig. 2 b) (vs. abdomen partially or completely covered by plates, Figs. 2 c,d, respectively). Moreover, Hisonotus alberti differs from H. bocaiuva , H. carreiro , H. francirochai , H. iota , H. leucophrys and H. prata by the absence of a conspicuous tuft of enlarged odontodes on posterior tip of parieto-supraoccipital (vs. presence); from H. chromodontus , H. acuen , H. vespuccii and H. bockmanni by possessing a rectangular dorsal-fin spinelet (vs. a functional V -shaped spinelet); from H. leucophrys , H. megaloplax , H. montanus , H. nigricauda , H. laevior , H. notopagos , H. carreiro , H. prata , H. vireo , H. brunneus , H. heterogaster , and H. bocaiuva by possessing a complete mid-lateral plate series (i.e., plate series not truncated), Fig. 3 b (vs. mid-lateral plate series incomplete and truncated); from H. megaloplax , H. montanus , H. nigricauda , H. carreiro , H. prata , H. brunneus , H. iota , H. acuen , and H. bocaiuva by larger number of vertebrae (29–30 vs. 25–28); from H. nigricauda and H. prata , H. leucofrenatus , and H. notatus by possessing a dark brown pigmented caudal fin with paired rounded regions of hyaline color near the center of both caudal lobes ( Fig. 1 ) (vs. almost completely dark caudal fin); from H. leucophrys and H. montanus by absence of broad light stripes on dorsolateral surface of head (vs. presence of broad stripes on dorsolateral surface of head); from H. vespuccii by possessing non longitudinally aligned rows of odontodes on head and trunk (vs. odontodes forming longitudinally aligned rows); and from H. chromodontus by possessing yellow teeth apices (vs. reddish-brown teeth).

Description. Morphometric and meristic data are presented in Table 1. Small body size, holotype 33.5 mm SL; paratypes 26.3−34.1 mm SL. Body slender, dorsoventrally depressed, widest near cleithrum. Dorsally, tip of snout rounded, short (45.0−50.2% of HL), and depressed directly in front of each nostril on dorsal surface. Greatest body depth at dorsal fin origin (14.9−19.7% of SL) and greatest body width at cleithral region (22.3−26.1% of SL), gradually decreasing towards snout and caudal fin. In lateral view, dorsal profile of head angled upwards linearly from tip of snout to interocular area, shallowly concaved from interocular region to dorsal fin insertion. Dorsal profile of trunk nearly straight, descending from base of dorsal-fin origin to caudal peduncle. Ventral profile slightly concave from snout tip to anal-fin origin, linear from anal-fin origin to caudal peduncle.

Head without conspicuous crests, except a small tuft of enlarged odontodes on posterior tip of the parietosupraoccipital (more evident in juvenile specimens). Anterior margin of snout completely covered by dorsal and ventral series of odontodes; odontodes on tip of snout larger than on rest of head. Snout tip with delicate band lacking odontodes (not present in some specimens). Odontodes on head and trunk well defined, not forming longitudinal rows. Eyes small (14.1−20.9% of HL), dorsolaterally positioned. Lips round and papillose; papillae uniformly distributed on base of dentary and premaxilla, tapering distally. Lower lip larger than upper lip; lower and upper lip margins fringed. Maxillary barbel present and poorly developed. Teeth slender and bicuspid; medial cusp larger than lateral cusp. Left premaxillary teeth 14−22 (mode 20). Left dentary teeth 13−21 (mode 18).

Dorsal fin ii,7; dorsal-fin spinelet short and laterally extended ( Fig. 3 a); dorsal-fin locking mechanism not functional. Dorsal-fin origin posterior to pelvic-fin origin. Tip of branched dorsal-fin rays reaching vertical line through center of anal-fin base. Pectoral fin i,6; tip of longest pectoral-fin ray almost reaching vertical line through center of horizontal pelvic-fin length when depressed. Pectoral axial slit present between pectoral-fin base and lateral process of cleithrum. Anteroventral margin of pectoral spine possessing odontodes. Pelvic fin i,5; tip not exceeding anal-fin origin when depressed (in both sexes). Males with soft tissue flap along dorsal margin of unbranched pelvic-fin ray. Anal fin i,5; tip of unbranched anal-fin ray reaching 7th and 8th plate from anal-fin origin. Caudal fin i,14,i; distal margin forked. Cross-section of caudal peduncle near ellipsoid. Adipose fin absent. Total vertebrae 29 (3 C&S)−30 (1 C&S).

Body mostly covered by dermal plates. Ventral margin of head, small area around pectoral and pelvic fin origins, narrow band along dorsal-fin base, and abdominal region all lacking plates ( Fig. 2 a); minute platelets on pre-anal area rarely present ( Fig. 2 b). Cleithrum and coracoid partially to completely exposed in some specimens. Arrector fossae partially enclosed by ventral lamina of coracoids. Lateral side of body completely covered by plates; mid-dorsal and mid-ventral series of plates well developed, reaching center of caudal peduncle; median plates continuous through median portion of body, with 1 or 2 plates unperforated prior to termination of plate series ( Fig. 3 b).

Details of osteological features of the head are shown in Fig. 3 c in dorsal view. Snout tip formed by one square rostral plate (r). Parallelogram-shaped nasal plate (n) forming medial border of nostril and extending anteriorly and medially with several prenasal plates (pn). Prenasal plates formed by three to four polyhedric and variable plates, extending posteriorly to nostrils and nasal plates, anteriorly with rostral plate (n), and laterally with first postrostral plate. Prenasals present between nares comprised of small platelets and one large triangular shaped plate. Posterodorsal head plates consisting of compound pterotic (cpt), parieto-supraoccipital (soc), frontal (f), prefrontal (pf) and sphenotic (sp) plates. Compound pterotic (cpt) plates bearing relatively large and irregularly distributed fenestra. Details of osteological features of the head are shown in Fig. 3 d in lateral view. First posterior rostrum plate (pr1) rectangular in shape; Second posterior rostrum plate (pr2) and third posterior rostrum plate (pr3) larger than pr1, triangular and roughly pentagonal in shape, respectively. Complete series of canal-bearing infraorbital plates (io1-io5); io1 positioned between pr1 and pr2; io2 positioned between each nostril and pr2; pr3, pr4 and pr5 forming ventral and posterior limit of orbit. Canal-bearing preopercle (pop) elongate, positioned anterior to pr3, dorsal to io4 and io5, posterior to cp2, and ventral to first subocular check plate (cp1). First and second subocular cheek plates (cp1−cp2) and opercle (op) form posteriolateral margin of head.

Coloration in alcohol. Dorsal surface dark brown on head to light brown on margins of trunk (juveniles lighter than adults). Ventral surface light brown to yellow in juveniles. Body and fins covered by scattered chromatophores, which are more visible on dorsal and lateral portions of head ( Fig. 1 ). Caudal fin black from fin base to tip of rays, except extended hyaline area on dorsal lobe and hyaline spot on ventral lobe.

Sexual dimorphism. Males possess urogenital papillae and soft-tissue flaps along the shaft of the unbranched pelvic fin-ray, conditions that are not observed in females. Narial openings appear to be wider in males than females (mean: 12.4 % of HL in males vs. 10.7 % of HL in females).

Distribution and Habitat. The new species Hisonotus alberti is known from two tributaries of the upper rio Paraná basin: ribeirão das Posses and córrego Caxambú, and one tributary of the upper rio São Francisco basin at córrego Luciano ( Fig. 4 ). The new species is found to be associated with marginal vegetation.

Etymology. The specific epithet “ alberti ” is a patronym honoring professor James S. Albert, from the University of Louisiana at Lafayette (UL) in recognition of his dedication and contributions to the studies of Neotropical freshwater fishes.

Figures

FIGURE 1. Hisonotus alberti, holotype, MZUSP 118845, male, 33.5 mm SL, from ribeirão das Posses, upper rio Paraná basin in municipality of São Roque de Minas, Brazil.

FIGURE 2. Cleared and stained images showing the variation in abdominal plates. (a) Hisonotus alberti, LBP 10266, 32.1 mm SL, abdomen completely exposed, with absence of dermal plates; (b) H. alberti, LBP 10266, 31.5 mm SL, abdomen with extremely small plate (black arrow) near the urogenital opening; (c) H. chromodontus, LBP 7948, 23.1 mm SL, abdomen partially covered by plates; (d) H. chromodontus, LBP 7948, 27.2 mm SL, abdomen completely covered by plates.

FIGURE 3. Hisonotus alberti, paratype, LBP 10266, 32.1 mm SL, sex not determined. (a) Dorsal view illustrating the rectangular shape of the spinelet; (b) Lateral view illustrating lateral trunk plates; (c) dorsal and (d) lateral views illustrating the configuration of cranial bones and dermal plates of the head.

FIGURE 4. Distribution map of Hisonotus alberti in the upper rio Paraná basin (red) and upper rio São Francisco basin (yellow). The green dot represents the type locality at ribeirão das Posses, municipality of São Roque de Minas, 20 ° 17 ' 15 " S, 46 ° 34 ' 53 " W. The blue dots represent paratype localities.