Ammoglanis obliquus, Henschel & Bragança & Rangel-Pereira & Costa, 2020

Henschel, Elisabeth, Braganca, Pedro H. N., Rangel-Pereira, Filipe & Costa, Wilson J. E. M., 2020, A new psammophilic species of the catfish genus Ammoglanis (Siluriformes, Trichomycteridae) from the Amazon River basin, northern Brazil, Zoosystematics and Evolution 96 (1), pp. 67-72 : 67

Ammoglanis obliquus sp. nov. Fig. 1A, B , 2 , Table 1

Holotype.

UFRJ 12477, 14.1 mm SL; Brazil: Amazonas state: Rio Preto da Eva municipality: sandbank at small stream, Preto da Eva River drainage, Amazonas river basin, 02°46'27"S, 59°38'58"W, altitude about 20 m a.s.l.; collected by E. Henschel, P. Bragança and F. Rangel-Pereira, 28 August 2019.

Paratypes.

UFRJ 12448, 25, 12.0-15.5 mm SL; UFRJ 12479, 4, 12.8-13.2 mm SL; UFRJ 12478, 4 (CS), 13.0-14.1 mm SL; INPA 59277, 2, 12.8-12.9 mm SL; all collected with holotype.

Diagnosis.

Ammoglanis obliquus differs from all its congeners except A. pulex by the presence of seven diagonal rows of dark cromatophores forming a banded pattern on flank of live specimens (vs trunk with three longitudinal rows of dark chromatophores in A. diaphanus and A. amapaensis , or whitish with few minute dark chromatophores scattered on body in A. multidentatus ), the absence of metapterygoid (Fig. 3 ; vs presence), and by the presence of two finger-like projections on chin region ( de Pinna and Winemiller 2000: fig. 2b; vs absence). It is distinguished from A. pulex by the presence of dentary teeth (Fig. 4A ; vs absence), the presence of premaxillary teeth (Fig. 4B ; vs absence), by having 6+6 caudal-fin rays (vs 5+5), and by the absence of the pelvic splint (vs presence). It further differs from A. diaphanus , A. amapaensis , and A. multidentatus by the absence of the sesamoid supraorbital (Fig. 5 , vs presence), by having fewer premaxillary teeth (3 vs 9-12 in A. diaphanus , 8-11 in A. amapaensis , and 10 or 11 in A. multidentatus ), fewer dentary teeth (4 vs 8 in A. diaphanus , 7 or 8 in A. amapaensis , and 11-13 in A. multidentatus ), and fewer dorsal-fin rays (total of 8 vs 10 in A. diaphanus , 9 in A. amapaensis , and A. multidentatus ). It is distinguished from A. diaphanus and A. multidentatus by the presence of 6 pectoral-fin rays (vs 7 in A. diaphanus and 7 or 8 in A. multidentatus ), and the presence of a scythe-shaped antorbital (vs antorbital straight, with its tip not curved mesially); from A. amapaensis , by the presence of a wide cranial fontanel (vs dorsal surface of the neurocranium totally ossified, without a fontanel; Mattos et al. 2008: fig. 4), absence of separate ossification of the anterior cartilage of autopalatine (vs presence); from A. multidentatus , by possessing fewer opercular odontodes (8-11 vs 15 or 16), fewer interopercular odontodes (5-8 vs 10 or 11), fewer anal-fin rays (total of 8 vs 9), and fewer pelvic-fin rays (total of 4 or 5 vs 6).

Description.

Morphometric data in Table 1 . Dorsal profile of body convex from tip of snout to midline of trunk and slightly convex from that point to base of caudal fin. Ventral body profile convex from mouth to point at vertical through pectoral-fin origin; slightly convex from that point to origin of caudal peduncle; slightly convex from origin of caudal peduncle to caudal-fin origin. Caudal peduncle strongly compressed. Urogenital opening at vertical posterior to dorsal-fin origin. Head triangular in dorsal view, depressed, broader than long. Eye elliptical, laterally positioned on head. Anterior profile of snout rounded. Mouth subterminal and crescent-shaped. Nasal barbel reaching posterior margin of eye. Maxillary barbel extending to posterior border of interopercular patch of odontodes. Rictal barbel reaching middle of interopercular patch of odontodes. Chin region with two finger-like projections. Teeth conical, three on premaxilla, irregularly arranged in a single row; four on dentary arranged in a single row. Opercular and interopercular patches of odontodes elliptical; opercular odontodes 8-11; interopercular odontodes 5-8. Opercular and interopercular odontodes conical, tips of odontodes curved dorsomedially. Cranial fontanel wide, lozenge-shaped, delimited anteriorly by mesethmoid and frontal and posteriorly by sphenotic and supraoccipital.

Dorsal fin subtriangular; dorsal-fin rays ii,6. Dorsal-fin first pterygiophore posterior to neural spines of 18th vertebra; tip of its last pterygiophore immediately anterior to neural spine of 21th vertebra. Seven dorsal-fin pterygiophores. Anal fin subtriangular, its origin at vertical posterior to dorsal-fin base; anal-fin rays ii,5 plus one rudimentary ray on fin origin. Anal-fin first pterygiophore posterior to neural spines of 20th or 21st vertebra; tip of its last pterygiophore immediately anterior to neural spine of 24th vertebra. Six anal-fin pterygiophores. Origin of anal fin in a vertical through origin of first or second branched dorsal-fin ray. Caudal fin subtruncate; principal caudal-fin rays ii,4+4,ii. Dorsal procurrent caudal-fin rays 6 or 7; ventral procurrent caudal-fin rays 7. Both caudal-fin lobes with four branched rays. Middle rays of caudal fin branched once. Parhypural and hypurals 1 and 2 fused and bearing six rays. Hypurals 3, 4, and 5 fused to each other, bearing six rays. Neural arch of compound centrum incomplete. Uroneural thin and elongate. Pelvic fin slightly pointed, its tip reaching vertical through origin of dorsal-fin base, pelvic-fin bases medially separated by interspace nearly equal to pelvic-fin base width; pelvic-fin rays i,2,i (2) or i,2,ii (2). Pelvic-fin origin in vertical through base of hemal spine of 11th or 12th vertebra. Pectoral fin approximately subtriangular in dorsal view, first pectoral-fin ray terminating in long filament reaching about 50% of pectoral-fin length without filament; pectoral-fin rays i,5. Vertebrae 34 or 35; ribs two.

Mesethmoidal region and adjacent structures (Fig. 5).

Anterior margin of mesethmoid slightly concave. Antorbital scythe-shaped in dorsal view; sesamoid supraorbital absent. Premaxilla without prominent lateral process, but with distal portion pointed. Maxilla slender, twice longer than premaxilla. Autopalatine approximately rectangular; latero-posterior process of autopalatine short; cartilaginous head of autopalatine long, about one-third of autopalatine; anterior autopalatine ossification absent.

Suspensorium and opercular apparatus (Fig. 3).

Metapterygoid absent. Quadrate long and slender, its length about 75% length of hyomandibula without anterior process, its depth about 30% to quadrate total length; postero-dorsal process of quadrate absent. Hyomandibula with narrow, pointed anteriorly directed process, its length about 67% hyomandibula longitudinal length excluding process, its tip anteriorly reaching vertical through anterior half of quadrate. Interopercle compact, without anterior projection. Opercle robust, its greatest depth about 40% of its length, excluding processes and odontodes patch; anteroventral process of opercle long, its length about 75% length of opercle main axis excluding odontode patch.

Colouration in life.

Head integument and musculature transparent, pinkish colouration from blood vessels visible by transparency. Dorsal surface of head and dorso-lateral surface of body with dark chromatophores scattered over snout and distal portion of premaxilla, internal pigmentation from brain case visible mainly by transparency. Head ventral and ventro-lateral surfaces with few dark chromatophores, mostly forming small patches. Eyes black. Barbels transparent with few minute internal chromatophores over support cartilage. Trunk transparent with lipid grains visible along visceral cavity and dorsal midline. Pinkish colouration from blood vessels visible by transparency. Dorsal surface with dark chromatophores grouped in regular intervals, forming seven poorly-defined blotches. Trunk lateral surface with scattered dark chromatophores arranged along midline, highly concentrated near caudal fin base, forming banded pattern. Trunk ventro-lateral surface with grouped inner dark chromatophores, forming seven diagonal bands. Vertebral column with dark colouration visible by transparency, arranged in regular intervals matching dorsal and ventro-lateral chromatophores and composing lateral portion of banded pattern. Fins hyaline, with few dark chromatophores scattered on caudal fin and at base of anal fin.

Colour in alcohol.

Ground colouration of trunk and head whitish, with few minute dark chromatophores on dorsum, flank, and head. Chromatophores concentrated forming a vertical band on base of caudal fin and in middle of caudal peduncle. Melanophores concentrated at regular intervals along dorsum, forming eight bands in dorsal view. Dark chromatophores in head concentrated in base of opercular patch of odontodes and in brain and snout area. Fins hyaline.

Distribution.

Known only from its type locality in Rio Preto da Eva drainage, Amazonas river basin, northern Brazil.

Etymology.

From the Latin obliquus , meaning oblique, referring to the conspicuous diagonal banded colouration pattern of living specimens.

Ecological notes.

This species is known only from a small clearwater tributary of Preto da Eva river, which is a left margin tributary of the Amazonas river. Individuals were found associated with a sand-bank lying on the centre of an artificial widening of the main course, next to a road. The stream course margins were lined by gallery rainforest, and the water column was about 1 m deep with a weak current. The sand-bank was composed of coarse, yellow sand and with sparse patches of small banks of macrophytes. Capture was accomplished by scooping of the superficial layer of sand with fine hand-nets. Specimens of Potamoglanis Henschel, Mattos, Katz & Costa, 2018 and Ammocryptocharax Weitzman & Kanazawa, 1976 were frequently captured together with Ammoglanis obliquus . This area as a whole is under high deforestation pressure due to local human occupation.

Figures

Figure 1. Ammoglanis obliquus: UFRJ 12477, 14.1 mm SL (holotype): Amazonas river basin. A. Lateral left view; B. Dorsal view.

Figure 2. Live specimen of Ammoglanis obliquus: UFRJ 12448; 13.0 mm SL.

Figure 3. Ammoglanis obliquus, UFRJ 12478, 13.2 mm SL; lateral view of the left suspensorium and opercular apparatus. APO - anteroventral process of opercle length; OML - opercular main axis length.

Figure 4. Ammoglanis obliquus, UFRJ 12478, 13.2 mm SL. A. Ventral view of the left premaxilla; B. Medial view of left lower jaw.

Figure 5. Ammoglanis obliquus, UFRJ 12478, 13.2 mm SL; dorsal view of mesethmoidal region and associated structures.