Rhinotocinclus pilosus, Reis & Lehmann, 2022

Reis, Roberto E. & Lehmann A., Pablo, 2022, A new genus of armored catfish (Siluriformes: Loricariidae) from the Greater Amazon, with a review of the species and description of five new species, Neotropical Ichthyology (e 220002) 20 (2), pp. 1-100 : 47-51

Rhinotocinclus pilosus , new species urn:lsid:zoobank.org:act:5D604B71-5C91-4452-BB9F-5CA4CF804ED2

( Figs. 27–28 ; Tab. 5 )

Holotype. UFRO-ICT 27700 , 22.6 mm SL, igarapé Traíra , ca. 35 km E of rio Madeira on Transamazon road, Humaitá, Amazonas, Brazil, 07°35’30.9”S 62°44’45.4”W, 8 Aug 2012, W. M. Ohara.

Paratypes. Amazonas State, Brazil: INPA 59644 , 3, 15.7–20.6 mm SL (1 measured, 20.6 mm SL), MCP 54753 , 10, 15.0– 21.8 mm SL (7 measured, 19.1–21.8 mm SL), ROM 111485 , 2, 17.9–20.1 mm SL (1 measured, 20.1 mm SL), UFRO-ICT 23448 , 16, 13.2–20.9 mm SL (5 measured, 19.2-20.9 mm SL), collected with holotype . MCP 35874 , 1, 19.9 mm SL (measured), creek crossing Transamazon road ca. 68 km E of rio Madeira , Humaitá, 07°43’58”S 62°29’40”W, 27 Jul 2004, R. Reis, F. Langeani, E. Pereira & A. Cardoso. MCP 35875 , 3, 14.1–14.6 mm SL + 2 cs, igarapé Traíra , ca. 35 km E of rio Madeira on Transamazon road, Humaitá, 07°35’33”S 62°44’45”W, 27 Jul 2004, R. Reis, F. Langeani, E. Pereira & A. Cardoso. MCP 35878 , 3, 15.2–19.1 mm SL (1 measured, 19.1 mm SL) + 1 cs, rio Maicimirim , ca. 45 km E of rio Madeira on Transamazon road, Humaitá, 07°37’56”S 62°39’44”W, 27 Jul 2004, R. Reis, F. Langeani, E. Pereira & A. Cardoso. UFRO-ICT 17593 , 1, 15.1 mm SL, flooded area in right bank of rio Marmelos , Humaitá, 07°33’22.4”S 62°42’59.9”W, 10 Aug 2012, W. Ohara. UFRO-ICT 18382 , 11, 15.0–21.0 mm SL (3 measured, 18.1–21.0 mm SL), rio Marmelos , Humaitá, 07°33’22.4”S 62°42’59.9”W, 10 Aug 2012, LIP team col.

Diagnosis. Rhinotocinclus pilosus is distinguished from R. acuen , R. bockmanni , R. chromodontus , R. dani , R. dinizae , R. hera , R. jumaorum , R. loxochelis n. sp., R. marginalis n. sp., and R. pentakelis by possessing an adipose fin (vs. adipose fin absent), and by having a Y-shaped light mark from the snout tip to each nostril (Figs. 6A,B; vs. light mark V-shaped or present as two separate lines from snout tip diverging to each nostril). It is distinguished from R. collinsae , R. halbolthi , and R. hardmanni by lacking accessory teeth on both premaxilla and dentary (Figs. 5B, C; vs. accessory teeth present, Fig. 5A); the odontodes on the ventral surface of first pelvic-fin ray bent and pointing mesially (Fig. 9A; vs. odontodes aligned with main ray axis, Fig. 9B); a triangular dark spot on the anterior portion of the dorsal-fin membrane (Fig. 8B; vs. dorsal-fin spot absent); a Y-shaped light mark from snout tip to nostrils (vs. Y-shaped light mark absent); and a larger orbit, 27.1–34.9% snout length (vs. orbit 18.9–24.6% snout length). Rhinotocinclus pilosus is distinguished from R. britskii , R. discolor , R. eppleyi , R. isabelae n. sp., R. kwarup , R. longirostris , R. polyochrus , R. variola , and R. yaka by having the belly naked or almost naked between lateral abdominal plates, with none or one row of granular platelets in the middle (Fig. 10C; vs. belly fully plated, Figs. 10A,B). It is further distinguished from the species above except R. isabelae n. sp., by having 1–2 lateral abdominal plates (vs. 3–6 plates); and from R. isabelae n. sp. by the shallower caudal peduncle (6.3–7.5% vs. 8.1–8.8% SL), and by having 31–37 premaxillary teeth (vs. 21–29 teeth).

Description. Proportional measurements in Tab. 5 . Dorsal profile of head straight to slightly concave from snout tip to area between nares, straight between orbits and convex from that point to parieto-supraoccipital tip; straight to slightly convex from that point to origin of dorsal fin. Dorsal profile of body mostly straight and descending from dorsal-fin origin to insertion of caudal fin. Trunk horizontally ovoid to roundly triangular and caudal peduncle vertically ovoid in cross section, vaguely flattened ventrally and compressed caudally. Body progressively narrowing posteriorly from cleithrum, more so behind dorsal fin.

Head widely flat between orbits; dorsal margin of orbit slightly elevated. Snout elongated, depressed, anterior margin rounded in dorsal view, with small depression anterior to naris. Snout quickly becoming wide, sides of head becoming more parallel at level of second postrostral plate. Eye comparatively small, positioned dorsolaterally, with small to medium dorsal iris operculum. Posterior tip of parieto-supraoccipital with two keels of enlarged odontodes, disappearing in larger specimens. Slightly enlarged odontodes on snout border, especially on rostral and postrostral plates and on lower surface of pectoral and pelvic spines; enlarged odontodes curved and posteriorly oriented. Odontodes on trunk and fins, especially posterior to dorsal fin, elongate and acicular, giving hairy appearance. Canal cheek plate bent and elongated posteroventrally, contacting cleithum. Lips rounded, narrow, covered with minute papillae; papillae slightly decreasing in size towards lip margin. Lip margin with uniformly distributed papillae forming delicate fringe. Maxillary barbel mostly adnate to lower lip with small free distal portion. Teeth moderately slender, bifid. Larger, medial cusp blade-like and slightly rounded, not elongated. Smaller, lateral cusp minute and pointed. Premaxillary teeth 31–37 (35); dentary teeth 29–35 (34); accessory teeth absent.

Body entirely covered by dermal plates except for ventral surface of head around lips, abdomen between lateral abdominal plates, and area around anus. Few plateles sometimes present in single, irregular series in middle abdomen or in preanal area. Lateral plates arranged in five longitudinal series on trunk. Dorsal plate series complete, beginning at origin of dorsal fin, with 20 plates; mid-dorsal series incomplete, with 5–6 plates; middle series complete, with two ossified tubes and 23 plates. Lateral line on middle plate series with two ossified tubes, 20–22 plates bearing canal, and 1–3 terminal plates without canal. Mid-ventral series incomplete with 16 plates; series terminating below adipose fin. Ventral series complete and continuous from pelvic-fin origin to caudal-fin base, with 17 plates. Predorsal plates forming two transverse rows anterior to nuchal plate. Preadipose azygous plates 1–2. Coracoid almost completely exposed ventrally, with medial portion covered with skin, somewhat longer than cleithrum; cleithrum exposed laterally with medial area and arrector fossa covered by skin. Lateral abdominal plates 1–2 (2/1); plates small, transversely elongate to rounded, close to coracoid. Middle abdominal plates zero to one series of small platelets embedded in skin in middle of abdomen. Preanal plate absent, none to five platelets embedded in skin in preanal area. First anal-fin pterygiophore exposed in front of anal-fin as small, plate-like bone supporting odontodes. Total vertebrae 27, in two dissected specimens.

Dorsal-fin rays I,7; spine slightly arched. Dorsal-fin origin slightly posterior to vertical through pelvic-fin origin. Dorsal-fin spinelet present, plate-like, roundly triangular dorsally and V-shaped anteriorly. Spinelet articulated to first dorsal-fin pterygiophore and dorsal-fin spine locking mechanism functional. Adipose fin present and well developed. Pectoral-fin rays I,6. Large spine straight to slightly arched; tip of adpressed spine reaching between distal third and distal fourth of pelvic fin. Pectoralfin axillary slit present, with large slanted opening ventral to tip of posterior process of cleithrum. Pelvic-fin rays i,5, unbranbched ray shorter than branched rays, especially in females; fin short, with tip of adpressed fin falling short of anal-fin origin in both males and females. Adult males with low fleshy flap along posterodorsal margin of thickened first pelvic-fin ray. Odontodes on ventral surface of thickened first pelvic-fin ray strongly bent and oriented mesially. Anal-fin rays i,5. Caudal-fin rays i,14,i, with lower unbranched ray slightly longer than, or equal to upper.

Color in alcohol. Dorsal portions of head and trunk light brown, lighter laterally, and cream to pale yellow ventrally. Dorsal and lateral surface of snout with patches of dark chromatophores forming dark brown lines. Light Y-shaped mark from snout tip diverging towards nostrils. Compound pterotic and most of parieto-supraoccipial behind eyes dark brown. Posterior tip of parieto-supraoccipital and predorsal region lighter than surrounding areas, but not forming inverted Y-shaped mark. Trunk with four conspicuous dark brown bars; bars 1 and 2 coalesced in wider bar. Bars extending transversely from dorsal midline and narrowing ventrally, ventral tip of bar 2 reaching to ventral midline. Ventral surface mostly unpigmented, but small dark chromatophores scattered on cheeks, abdomen, and caudal peduncle. Tooth cusps reddish brown. Fins with transverse, conspicuous brown bands formed by concentration of chromatophores on rays; bands more numerous on leading rays; membranes mostly hyaline. Dorsal fin with dark triangular spot on anterior portion, spine with 4–5 dark brown spots, branched rays with one inconspicuous dark band on distal half. Pectoral-fin spine homogeneously dusky or with 4–5 incospicuous dark spots, branched rays with 2 irregular dark bands. Pelvic fin with 2 irregular dark bands. Anal fin with 1–2 dark bands. Adipose fin with 1 dark spot on anterior portion of spine. Caudal fin with dark transverse blotch at base and melanophores scattered on branched rays, forming incospicuous dark brown band on posterior third.

Sexual dimorphism. Males have a small urogenital papilla immediately behind the anus and a low skin fold along the first, unbranched pelvic-fin ray, both characteristics being absent in females. Males also have slightly longer pelvic-fin unbranched ray which is almost as long as first branched ray; in females unbranched ray in clearly shorter than first unbranched ray. Males also possess a slightly larger nostril than females.

Geographical distribution. Rhinotocinclus pilosus is known from few localities in creeks tributary to the rio Madeira east of Humaitá, Amazonas, Brazil ( Fig. 15 ).

Etymology. Rhinotocinclus pilosus from the Latin pilosus , meaning hairy, in allusion to the dense cover of hyperthrophied odontodes typical of the species. An adjective.

Conservation status. The extinction risk of Rhinotocinclus pilosus is assessed as low despite its restricted range and the limited knowledge of its geographic distribution. The species is so far known from few localities near Humaitá, Amazonas State of Brazil, with an Extension of Occurrence (EOO) estimated by the convex polygon of those localities of approximately 82 km 2. Despite being crossed by the Trans-Amazon road, where most specimens were collected, the region is relatively well preserved and surrounded by protected areas (Humaitá National Forest south of the Trans-Amazon road and the Indigenous Lands Nove de Janeiro, Pirahã, and Ipixuna north of the road). Despite logging, gold mining, and cattle ranching are common throughout the TransAmazon road, these threats are not believed to impact the species. For this reason, R. pilosus is preliminarily categorized as Least Concern (LC) according to the International Union for Conservation of Nature (IUCN) categories and criteria (IUCN Standards and Petitions Subcommittee, 2019).

Figures

FIGURE 15 | Geographical distribution of Rhinotocinclus species of the R. britskii group in central and northwestern South America. Rhinotocinclus britskii (white dots); R. discolor n. sp. (purple dots); R. eppleyi (orange dots); R. isabelae n. sp. (pink dots); R. kwarup (red dots); R. longirostris (blue dots); R. pilosus n. sp. (yellow dots); R. polyochrus (cyan dot); R. variola (black dots); R. yaka (light green dots). T = Type-locality; T1 = type-locality of Parotocinclus britskii, T2 = type-locality of P. amazonensis, T3 = type-locality of P. aripuanensis.

FIGURE 27 | Rhinotocinclus pilosus, holotype, UFRO 27700, 22.6 mm SL, female, igarapé Traíra, ca. 35 km E of rio Madeira on Transamazon road, Humaitá, Amazonas, Brazil.

FIGURE 28 | Live specimen of Rhinotocinclus pilosus from lot MCP 35878, rio Maicimirim, ca. 45 km E of rio Madeira on Transamazon road, Humaitá, Amazonas, Brazil.