Ammoglanis nheengatu, Canto & Hercos & Ribeiro, 2022

Canto, André L. Colares, Hercos, Alexandre P. & Ribeiro, Frank Raynner V., 2022, Description of a new species of miniature catfish of the genus Ammoglanis (Siluriformes: Trichomycteridae) from rio Tapajós basin, Brazil, Neotropical Ichthyology (e 210122) 20 (2), pp. 1-13 : 3-9

Ammoglanis nheengatu , new species urn:lsid:zoobank.org:act:BDFDB93A-BC59-4520-A7B6-859D79109F65

( Fig. 1 ; Tab. 1)

Holotype. INPA 59653 , 14.8 mm SL, Brazil, Pará State, Itaituba Municipality, rio Tapajós basin, rio Jamanxim drainage, igarapé Branco , tributary to Aruri Grande , 05°24’9.07”S 55°52’59.01”W, 9 Out 2019, A. P. Hercos.

Paratypes. All collected with holotype. IDSM 3063 , 5 , 13.1–14.9 mm SL; INPA

59654, 3, 12.8–12.9 mm SL; UFOPA-I 1357, 10, 5 CS, 10.9–16.8 mm SL.

Diagnosis. Ammoglanis nheengatu is distinguished from A. diaphanus , A. amapaensis , and A. multidentatus by the absence (vs. presence) of the metapterygoid; by the possession of eight or nine transverse dark bars regularly spaced on the dorsum, more visible in dorsal view (vs. three transversal dark bars regularly spaced along the dorsum in A. diaphanus and A. amapaensis and few dark chromatophores scattered on the body in A. multidentatus ), and the presence (vs. absence) of two small, finger-like papillae on chin anterior to the gular apex. Ammoglanis nheengatu is distinguished from A. pulex , A. natgeorum , and A. obliquus by having 8–10 teeth in the premaxilla (vs. teeth absent in A. pulex , 3 in A. obliquus , and 4–6 in A. natgeorum ) and presence (vs. absence) of a sesamoid supraorbital, and from A. obliquus and A. natgeorum by the presence (vs. absence) of a pelvic splint. Ammoglanis nheengatu further differs from A. natgeorum by having six or seven (vs. five) interopercular odontodes and five (vs. six) pectoral-fin rays; from A. amapaensis by the presence (vs. absence) of cranial fontanel and absence (vs. presence) of anterior autopalatine ossification; from A. multidentatus by having short posterolateral process of autopalatine (vs. slender and long) and 4 or 5 (vs. 6) pelvic-fin rays; and from A. diaphanus by having 8 (vs. 10) dorsal-fin rays and 31–32 (vs. 34) vertebrae ( Tab. 2).

Description. Morphometric data in Tab. 1. Body elongate; dorsal profile of head and body straight to slightly convex from tip of snout to origin of dorsal fin; approximately straight from end of dorsal-fin base to caudal-fin base. Ventral profile of head slightly convex. Ventral profile of trunk approximately straight up to insertion of anal fin; slightly convex from end of anal-fin base to caudal-fin base. Caudal peduncle strongly compressed. Urogenital and anal openings on vertical through base of first or second branched dorsal-fin rays. Head wide and depressed, trapezoidal in dorsal view. Eye small, elliptical, or nearly rounded, located dorsolaterally at anterior half of head length. Anterior profile of snout rounded. Mouth subterminal and small, with thin lower lip. Teeth conical, 8–10 in premaxilla and dentary, respectively, and arranged in two regular rows. Branchiostegal membranes attached to isthmus and branchial openings wide. Maxillary, rictal, and nasal barbels short, with thick base, tapered distally. Maxillary barbel extending to posterior border of interopercular patch of odontodes. Rictal barbel slightly shorter than maxillary barbel, reaching middle of interopercular patch of odontodes. Nasal barbel extending beyond posterior margin of eye, reaching vertical through base of interopercular patch of odontodes. Chin region with two finger-like projections, one on each side of midline. Opercular and interopercular patches of odontodes small, elliptical, and located dorsolaterally on head; 7–8 conical opercular odontodes; 6–7 conical interopercular odontodes. Opercular and interopercular odontodes gradually increasing in size posteriorly and with tips curved dorsomedially.

Pectoral-fin rays i,5. Fin subtriangular in dorsal view; first ray markedly longest. Pelvic fin with slightly rounded distal profile, reaching vertical through origin of dorsal-fin base. Pelvic-fin rays i,2,ii or i,3,i. Pelvic-fin origin at vertical through between haemal spine of 13 th and 14 th vertebra. Pelvic splint present. Dorsal fin with semicircular profile in lateral view. Dorsal-fin rays ii,4,ii or ii,5,i, with seven pterygiophores. First pterygiophore inserted posterior to neural spine of 15 th (2) or 16 th (3) vertebra; last pterygiophore anterior to neural spine of 19 th (3) or 20 th (2) vertebra. Anal fin with semicircular profile in lateral view, its origin at vertical through base of last rays of dorsal fin. Anal-fin rays ii,3,i or ii,4,i plus one rudimentary ray at fin origin. Six anal-fin pterygiophores, first pterygiophore posterior to haemal spine of 18 th (2) or 19 th (3) vertebra; last pterygiophore immediately anterior to haemal spine of 22 nd (4) or 23 rd (1) vertebra. Caudal fin moderately long, with rounded distal margin; principal caudal-fin rays ii,4+4,ii. Dorsal and ventral procurrent caudal-fin rays 7 or 8.

Osteology. Anterior margin of mesethmoid approximately straight to slightly concave in medial portion, mesethmoid cornua slender distally. Cranial fontanel lozenge-shaped, extending from anterior third of frontal to middle portion of parieto-supraoccipital ( Fig. 2 ). Antorbital anteriorly expanded scythe-shape. Sesamoid supraorbital present, approximately 70% of antorbital length ( Fig. 2 ).

Premaxilla with relatively long and pointed lateral process, projecting approximately 80% of bone length. Ventral expansion of premaxilla absent. Maxilla narrow and elongated, with short process dorsolaterally in anterior third. Autopalatine with rectangular shape; lateral margin concave, medial margin slightly convex. Posterolateral process of autopalatine short, posteroventrally curved. Anterior autopalatine ossification absent; cartilaginous head of palatine moderately large, about one-third of bone length.

Quadrate long, slender, about same length as longitudinal axis of hyomandibula. Very small process extending lateroventrally from anterior tip of quadrate, articulating with lower jaw; metapterygoid absent. Hyomandibula with elongated and narrow anterior process; its tip reaching vertical through anterior tip of quadrate ( Fig. 3 ). Anterior portion of interopercle anteriorly expanded. Three basibranchial elements, 2 nd and 3 rd ossified, 4 th cartilaginous. First hypobranchial ossified, 2 nd cartilaginous, with small osseous anterodistal process 3 rd, cartilaginous. Branchiostegal rays 6.

Vertebrae 32 (5 precaudal and 27 caudal vertebrae). Three pairs of pleural ribs, one specimen with third pair of ribs greatly reduced. Caudal skeleton composed of compound centrum, pleurostyle, and hypurals 3–5 fused, forming triangular upper hypural plate. Parhypural and hypurals 1–2 fused, forming trapezoidal lower hypural plate. Neural arch of compound centrum incomplete.

Coloration in alcohol. Body white to light yellow, darker dorsally. Dorsal region of head with patch of chromatophores, more concentrated on medial region, posterior to eye, extending up to nape and laterally to dorsal region of opercular odontodes. Ventral surface of head white, except for few sparse chromatophores on interopercular base. Barbels hyaline. Scattered dark chromatophores on sides of trunk, more concentrated along lateral midline. Chromatophores concentrated at regular intervals along dorsum, forming eight to nine dark bars, visible in dorsal view. Ventral region of caudal peduncle with chromatophores concentrated at regular intervals forming three bars. Dorsal-, caudal-, and anal-fins rays weakly pigmented by scattered chromatophores. Pelvic- and pectoral-fin rays hyaline. Some specimens with dark chromatophores concentrated on base of caudal-fin rays, forming two bands ( Fig. 1 ).

Coloration in life. Body semi-translucent; ground color lightly yellow, with dark chromatophores scattered along sides, more concentrated on lateral midline. Dorsal region of head with dark blotches on post-orbital and nuchal portions, extending laterally to dorsal region of opercular odontodes. Concentrated chromatophores extend from lateral edge of anterior nostril to anterior margin of eye, forming a dark stripe. Ventral surface of head with few dispersed chromatophores on branchiostegal membrane and interopercular base. Maxillary, rictal, and nasal barbels hyaline. Eight or nine transverse dark-brown bands on dorsal surface of body, extending from behind nape to caudal-fin base. Lateral surface of trunk with deeply set dark coloration, arranged at regular intervals, forming approximately seven dashes, only visible by transparency. Ventral surface of caudal peduncle with three transverse dark-brown bars. Dorsal-, caudal-, and anal-fin rays weakly pigmented by scattered chromatophores. Pelvic- and pectoral-fin rays hyaline. Dark chromatophores concentrated on base of caudal-fin rays, forming blotches ( Fig. 4 ).

Geographical distribution. Ammoglanis nheengatu is known only from its type locality, the igarapé Branco , a tributary to the rio Aruri Grande , rio Jamanxim drainage, a right bank tributary to the middle rio Tapajós, Pará State, Brazil ( Fig. 5 ) .

Etymology. The specific epithet, nheengatu , honors the indigenous people of the Amazon. Nheengatu is known as the general language of the Amazon that helped create the cultural identity of the largest Brazilian region. In the nineteenth century Nheengatu was the most commonly spoken language in the Amazon region, in both small and large cities (e.g., Belém, Manaus, Macapá, Santarém, Tefé, and Óbidos). Currently, Nheengatu is being rescued in indigenous schools of the lower rio Tapajós basin. A noun in apposition.

Ecological notes. Igarapé Branco, type locality of Ammoglanis nheengatu , is a “terra firme” clear water stream, approximately 9 m wide and 50 cm deep, with low flow speed. The collection site has large areas of riparian forest, with only part of the margins deforested for subsistence agriculture plantations. The specimens of A. nheengatu were captured only during the dry season, over sand banks (small beaches) located along the margin of the stream. The sand banks were composed of coarse yellow sand ( Fig. 6 ). The following physico-chemical water parameters were obtained at the collection site during the dry season of 2020: water temperature 24.9°C; pH 5.9; conductivity 27.4 µS/ cm3, and dissolved oxygen 5.88 mg /L. Ammoglanis nheengatu occurs syntopically with three others trichomycterids species: Ochmacanthus reinhardtii (Steindachner, 1882) , Stegophilus panzeri (Ahl, 1931) , and Tridentopsis sp.

Conservation status. The rio Jamanxim basin has been severely affected by anthropogenic pressures, including intense removal of native vegetation, mainly due to illegal logging, agricultural expansion, and gold mining activities ( Fearnside, 2015; Lobo et al., 2015). The type locality of the new species is located within an area impacted by the Cuiabá-Santarém highway (BR-163). However, the rio Aruri Grande basin drains into the Jamaxim National Park, an important protected biological reserve in western Pará. Along its margins, the rio Aruri Grande has many sandbanks, a favorable microhabitat for Ammoglanis nheengatu , suggesting that the species may occur inside the park. Therefore, following the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN, 2019), we propose that Ammoglanis nheengatu be categorized as Least Concern (LC).

Figures

FIGURE 1 | Ammoglanis nheengatu in lateral and dorsal views, holotype, INPA 59653, 14.8 mm SL, igarapé Branco, tributary to rio Aruri Grande, rio Jamanxim drainage, rio Tapajós basin, Pará State, Brazil.

FIGURE 2 | Neurocranium of Ammoglanis nheengatu, paratype, UFOPA–I 1357, 15.2 mm SL, in dorsal view.

FIGURE 3 | Left suspensorium of Ammoglanis nheengatu, paratype, UFOPA–I 1357, 15.2 mm SL, in lateral view.

FIGURE 4 | Live specimen of Ammoglanis nheengatu, paratype, UFOPA–I 1357, 16 mm SL.

FIGURE 5 | Map indicating the known distribution of Ammoglanis nheengatu in the igarapé Branco, tributary to rio Aruri Grande, rio Jamanxim drainage, rio Tapajós basin, Pará State, Brazil. Delimitation of the Jamanxim National Park in light green.

FIGURE 6 | Type-locality of Ammoglanis nheengatu, igarapé Branco, tributary to rio Aruri Grande, rio Jamanxim drainage, rio Tapajós basin, Itaituba municipality, Pará State, Brazil.