Gymnotocinclus anosteos, Carvalho & A. & Reis, 2008

Carvalho, Tiago Pinto, A., Pablo Lehmann & Reis, Roberto E., 2008, Gymnotocinclus anosteos, a new uniquely-plated genus and species of loricariid catfish (Teleostei: Siluriformes) from the upper rio Tocantins basin, central Brazil, Neotropical Ichthyology 6 (3), pp. 329-338 : 330-336

Gymnotocinclus anosteos , new species Figs. 1-2

Holotype. MCN 18624, 44.3 mm SL, male, Brazil, Goiás, Alto Paraíso de Goiás, ribeirão das Cobras, near to road GO-239, tributary to rio Tocantinzinho , rio Tocantins basin, 14º09’43"S 47º37’57"W, 9 Nov 1996, W. R. Koch & K. M. Grosser.

Paratypes. All from Brazil, Goiás, Alto Paraíso de Goiás. MCN 13543, 12 , 25.8-39.3 mm SL and MCP 41726, 5 , 22.1-41.6 mm SL + 3 c&s, 22.4-40.5 mm SL, collected with the holotype. MCN 13154, 7 , 16.3-34.3 mm SL, MCN 13155, 6 , 19.0- 31.6 mm SL, and ANSP 187156 , 5 , 22.5-40.8 mm SL, same locality as holotype, 4 Aug 1996, W. R. Koch, P. C. C. Milani & K. M. Grosser. MCN 13538, 1 , 28.1 mm SL, creek on road GO-239, tributary to rio Tocantinzinho , rio Tocantins basin, 14º08’22"S 47º39’45"W, 9 Nov 1996, W. R. Koch & K. M. Grosser .

Diagnosis. Same as for genus.

Description. Morphometrics and meristics given in Tables 1 and 2 respectively. Dorsal profile gently curved from snout tip to parieto-supraoccipital bone, almost straight from that point to dorsal-fin origin. Slightly concave to straight at dorsal-fin base. Straight from end of dorsal-fin base to caudal-fin origin. Ventral profile straight to slightly convex from snout tip to posterior border of lip, straight and posteroventrally sloped from that point to origin of pelvic fin, straight and posterodorsally inclined from pelvic fin to caudal-fin origin. Body flattened at predorsal region. Ventral surface of trunk flattened at base of paired fins. Caudal peduncle round in cross section. Greatest body depth at dorsal-fin origin. Least body depth at posterior end of caudal peduncle. Head and snout broad, snout anterior margin rounded in dorsal view. Body progressively narrowing posteriorly from cleithrum. Head flattened at parieto-supraoccipital, interorbital region straight. Upper margin of orbit not elevated. Eye small, dorsolaterally placed. Iris operculum small, less than half pupil diameter.

Pectoral fin I,6, posterior margin slightly rounded; when depressed reaching to middle of adpressed pelvic fin. Posterior margin of pectoral-fin spine smooth. Soft portion of pectoral spine large, about one-fourth of spine length. Pectoralfin axillary slit absent. Coracoid and cleithrum exposed laterally, supporting odontodes only in restricted lateral area near base of pectoral fin; covered by skin medially ( Fig. 6 ). Pelvic fin i,5, reaching anal-fin origin when depressed. Pelvic girdle with slender lateropterygium, club shaped, expanded proximally and thinner distally. Basipterygium ossified anteriorly, lacking anterior fenestrae ( Fig. 7 ). Dorsal fin II,7; spinelet present, reduced in size, quadrangular in shape. Nuchal plate present, triangular in shape. Dorsal-fin origin located posterior to vertical through pelvic-fin origin.Anal fin i,5, first analfin pterygiophore not exposed on ventral surface anterior to first anal-fin unbranched ray. Bifid hemal spines absent from abdominal vertebrae posterior to first anal-fin proximal radial. Caudal fin i,14,i. Compound hypurals 1 and 2 almost completely fused to the compound hypurals 3-5, posterior margin of caudal-fin skeleton with slight median notch. Total vertebrae 28-29 (3 c&s). Adipose fin absent, single series of three to six platelets at adipose fin position.

Head plates present, including postrostral plates, infraorbital series, cheek plates, and small scattered plates anterior to nostril. Body almost completely naked, without dermal plates ( Fig. 2 ), except for small platelets scattered all over body dorsal surface, not forming regular series; small platelets at lateral line composing median series; about six large plates on anterior portion of mid-ventral series; and last plates of ventral and dorsal series from adipose fin region to posterior end of caudal peduncle. Abdomen with scattered platelets irregularly arranged between posterior margin of coracoid and region anterior to anal-fin origin; abdominal platelets absent near pelvic-fin base. Fourth infraorbital not expanded ventrally, naked area below infraorbitals four and five and anterior to preopercle ( Fig. 8 ). Infraorbital canal entering infraorbital series via sphenotic. Canal-bearing cheek plate not extending medially in ventral view. Lateral line complete, without midbody gap. Raised odontodes absent from parieto-supraoccipital in adults, smaller juveniles with three raised crests of odontodes on posterior portion of parieto-supraoccipital. Odontodes on trunk with uniform size and distribution, not arranged into distinct rows, except for larger odontodes on ventral surface of pectoral-fin spine, and first pelvic- and anal-fin unbranched rays. Odontodes of pelvic fin turned mesially.Tip of odontodes on last lateral plates curved dorsally or anteriorly ( Fig. 4 ).

Anterior margin of mesethmoid rounded, not expanded laterally. Ventral surface of mesethmoid anterior to ventral articular condyle simple, without anteroventral lamina. Vertical lateral ethmoid ridge elevated, posterior portion contacting metapterygoid. Lateral ethmoid encapsulating nasal organ, with small longitudinal opening at lateral border of nasal capsule ( Fig. 5 ). Lateral ethmoid exposed on dorsal surface of head posterior to nostrils supporting one series of odontodes ( Fig. 8 ). Hyomandibula articular condyle contacting prootic. Compound pterotic not enlarged posterolaterally, posterior portion somewhat rounded, not pointed. Anteroventral margin of compound pterotic with irregularly arranged perforations of median to large size. Swimbladder capsule relatively enlarged, its posterior margin extending to joint of Weberian complex with

Character H N Low High Mean SD

Standard length (mm) 44.3 20 28.8 44.3 35.7 Percentages of standard length

Head length 33.0 20 32.5 34.4 33.3 0.56

Predorsal length 45.7 20 43.5 48.4 46.1 1.03

Dorsal-fin spine length 20.7 20 19.2 22.6 20.9 0.86

Anal-fin unbranched ray length 17.8 20 16.3 20.3 18.0 1.02

Pectoral-fin spine length 20.6 19 16.6 23.7 20.3 1.72

Pelvic-fin unbranched ray length 20.0 20 15.7 20.5 18.0 1.47

Cleithral width 26.7 20 24.6 27.0 25.8 0.71

Trunk length 17.0 20 15.2 17.3 16.2 0.71

Abdominal length 22.8 20 19.9 23.2 21.6 1.06

Body depth at dorsal-fin origin 19.1 20 16.4 19.7 17.5 0.86

Caudal-peduncle length 32.0 20 28.6 35.6 32.2 1.52

Caudal-peduncle depth 10.5 20 8.5 10.5 9.7 0.47 Percentages of head length

Snout length 58.6 20 54.7 62.0 57.9 1.87

Orbital diameter 14.0 20 12.6 16.7 14.5 1.04

Interorbital width 41.5 20 37.8 42.8 39.7 1.34

Head depth 50.8 20 43.4 50.9 48.1 1.75

Suborbital depth 28.5 20 20.7 28.5 24.7 2.18

Mandibular ramus 13.3 20 10.3 14.8 12.7 1.34

sixth centrum. Metapterygoid channel present, deep. Levator crest present, well developed, its extension not reaching dorsal portion of hyomandibula. Hyomandibula adductor crest present, extending from posterior corner of preopercle to dorsal articular condyle. Suture between metapterigoid and hyomandibula elongate, beginning almost on dorsal margin of bones ( Fig. 9 ). Preopercle laterosensorial canal straight, posterior ramus contacting hyomandibula adductor crest. Preopercle ventral margin straight, not reflected medially.

Teeth slender, bifid; major (medial) cusp slightly rounded and approximately three times longer than minor (lateral) cusp, minor cusp minute and pointed. Accessory teeth absent in premaxilla and dentary. Lips roundish, papillose, and comparatively large; anterior portion of lips well developed and fleshy, posterior portion almost reaching pectoral girdle. Maxillary barbel adnate, completely attached to lower lip.

Upper pharyngeal toothplate larger than fourth pharyngobranchial, which partially supports it.Accessory ceratobranchial flange present and well developed, almost same size of first ceratobranchial. Basibranchial 2 and 4 present. Basibranchial 2 partially ossified. Four branchiostegal rays ( Fig. 10 ).

Color in alcohol. Ground color of dorsal surface of head and body light to dark brown. Dorsal surface of head darker than body. Ventrolateral margins of head and trunk yellowish. Ventral surface yellowish and almost unpigmented. Wide longitudinal dark lateral stripe. Lateral line unpigmented, forming thin light longitudinal line in middle of dark lateral stripe. Four transverse dark saddles on dorsum, beginning at dark lateral longitudinal stripe and extending to middorsal line. Most anterior saddle inconspicuous, at dorsal-fin origin; second saddle beginning at end of dorsal-fin base and reaching vertical through second branched anal-fin ray; third saddle at typical adiposefin region; and posterior saddle at end of caudal peduncle. Pectoral and pelvic fins mostly hyaline, with few scattered chromatophores. Dorsal and anal fins with chromatophores forming two transverse dark bands, most conspicuous on dorsal fin. Caudal fin mostly dark, except for transverse hyaline band at middle and posterior end of rays. In some specimens, middle caudal rays darker forming longitudinal stripe.

Sexual dimorphism. Males with urogenital papilla just behind the anal opening. Adult males have a fleshy flap along the dorsal margin of the pelvic-fin thickened ray, which is wider basally and progressively narrowing distally. The flap is absent in juveniles and females.

Distribution. Gymnotocinclus anosteos is known only from two creeks, both tributaries to the rio Tocantinzinho, in the headwaters of the rio Tocantins basin, Goiás, Brazil ( Fig. 11 ).

Etymology. From the Greek anosteos , meaning boneless, in allusion to the absence of the lateral connecting bone.

Figures

Fig. 1. Gymnotocinclus anosteos, holotype, MCN 18624, male, 44.3 mm SL, ribeirão das Cobras, near highway GO-327, tributary of rio Tocantinzinho, rio Tocantins Basin, Alto Paraíso de Goiás, Goiás, Brazil.

Fig. 2. Gymnotocinclus anosteos, cleared and stained paratype, MCP 41726, male, 40.5 mm SL, collected with the holotype.

Fig. 6. Pectoral girdle in ventral view of Gymnotocinclus anosteos, MCP 41726, paratype, male, 40.5 mm.

Fig. 7. Pelvic girdle in dorsal view of Gymnotocinclus anosteos, MCP 41726, paratype, male, 40.5 mm.

Fig. 8. Skull in lateral view of Gymnotocinclus anosteos, MCP 41726, paratype, male, 40.5 mm.

Fig. 4. Scanning electron microscope image of dermal plates at posterior end of caudal peduncle. Gymnotocinclus anosteos, paratype, MCP 41726, male, 40.5 mm SL. LLP = lateral line plates, VPS = ventral plate series, DPS = dorsal plate series.Arrow indicates the modified odontode tips of the last plates on caudal peduncle.

Fig. 5. Left side of neurocranium in ventral view of Gymnotocinclus anosteos, MCP 41726, paratype, male, 40.5 mm.

Fig. 9. Suspensorium in lateral view of Gymnotocinclus anosteos, MCP 41726, paratype, male, 40.5 mm.

Fig. 10. Branchial skeleton in dorsal view of Gymnotocinclus anosteos, MCP 41726, paratype, male, 40.5 mm.

Fig. 11. Geographic distribution of Gymnotocinclus anosteos in the upper rio Tocantins drainage. Circles represent collecting sites, and T is the type-locality.