Rhinotocinclus loxochelis, 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 : 77-80

Rhinotocinclus loxochelis , new species urn:lsid:zoobank.org:act:1B9ABD2F-5756-49C4-AB59-3C15B820D98D

( Fig. 41 ; Tab. 8 )

Holotype. MPEG 38957 , 22.6 mm SL, creek in Jamanxim National Forest , Itaituba, Pará, 08°23’45.7”S 55°39’27.6”W, 28 May 2008, F. B. N. Ribeiro.

Paratypes. Rio Jamanxim basin, Pará State, Brazil: MPEG 15033 , 3, 17.4–23.1 mm SL (2 measured, 20.5–23.1 m SL) + 1 cs (measured, 22.4 mm SL), MCP 54747 , 2, 21.0– 22.6 mm SL (2 measured), collected with holotype . MPEG 17644 , 3, 20.3–21.4 mm SL (3 measured), rio Novo basin, tributary to rio Jamanxim, Jamanxim National Forest , Novo Progresso, 07°18’45.64”S 56°10’10.83”W, 24 Sep 2008, F. R. Silva . MPEG 17681 , 4, 20.2–21.6 mm SL, rio Claro, tributary to rio Jamanxim, Jamanxim National Forest , Novo Progresso, 07°02’50.6”S 55°47’12.5”W, 27 Aug 2008, F. R. Silva.

Diagnosis. Rhinotocinclus loxochelis is distinguished from all congeners by having the dominant color pattern formed by four dark bars on body somewhat fragmented and inclined, such that they connect to form a zig-zag pattern ( Fig. 41 ; vs. dominant color pattern formed by dark bars separated and distinct, or dark bars wide and partially coalesced, or formed by a dark stripe from the snout tip, through the eye and extending to end of caudal peduncle). Rhinotocinclus loxochelis is further distinguished from R. britskii , R. discolor , R. eppleyi , R. isabelae , R. kwarup , R. longirostris , R. pilosus , R. polyochrus , R. variola , and R. yaka by lacking an adipose fin (vs. adipose fin present). Rhinotocinclus loxochelis is further distinguished from congeners, except R. marginalis , R. bockmanni , R. dani , and R. pentakelis , by having small platelets at adipose-fin position (vs. small platelets absent). Rhinotocinclus loxochelis is distinguished from R. bockmanni by lacking a triangular dark spot at the dorsal-fin membrane (vs. dorsal-fin dark spot present), and from R. hera by having yellow teeth cusps (Fig. 5C; vs. light ochre cusps). Rhinotocinclus loxochelis is further distinguished from R. marginalis by the dark bar 2 on body reaching to the ventral midline (vs. dark bars on body barely passing lateral dark stripe), and by the deeper caudal peduncle 10.3–11.2% vs. 9.1–10.1% SL) and longer pectoral-fin spine (30.4–32.1% vs. 26.7–30.3% SL); and from R. dani by the deeper body (body depth 18.3–20.4% vs. 16.3–18.3% SL, caudal peduncle depth 10.3–11.2% vs. 8.8–9.9% SL, and head depth 44.9–49.4% vs. 38.0–43.5% HL).

Description. Proportional measurements in Tab. 8 . Dorsal profile of head slightly concave from snout tip to area between nares, convex from that point to parietosupraoccipital tip and 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 convex between orbits; dorsal margin of orbit not elevated. Snout elongated, depressed, its anterior margin rounded in dorsal view, with small depression anterior to naris. Eye comparatively large, positioned more laterally than dorsolaterally, with small dorsal iris operculum. Posterior tip of parieto-supraoccipital with patch of slightly enlarged odontodes. 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 head and trunk otherwise of uniform size and distribution. Canal cheek plate bent and elongated posteroventrally, almost 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 with large free distal portion. Fleshy keel on lower lip behind each dentary. Teeth moderately robust, bifid. Larger, medial cusp blade-like and slightly rounded, not elongated. Smaller, lateral cusp minute and pointed. Premaxillary teeth 16–22 (20); dentary teeth 15–19 (17); accessory teeth absent.

Body entirely covered by dermal plates except for ventral surface of head around lips, area around pelvic-fin insertion, and area around anus. Lateral plates arranged in five longitudinal series on trunk. Dorsal plate series complete, beginning at origin of dorsal fin, with 18 plates; mid-dorsal series incomplete, with 5–7 plates; middle series complete, with two ossified tubes and 22–23 plates. Lateral line on middle plate series with two ossified tubes, 21–22 pored plates followed by 1 terminal plate without canal. Mid-ventral series incomplete with 18 plates. Ventral series complete and continuous from pelvic-fin origin to caudal-fin base, with 19 plates. Predorsal plates forming two transverse rows anterior to nuchal plate. Coracoid completely exposed ventrally, twice longer than cleithrum; cleithrum exposed laterally with medial area and arrector fossa covered by skin. Lateral abdominal plates 3–5 (3/4); plates transversely elongate, clearly arranged in line between coracoid and pelvic-fin origin. Middle abdominal plates 1–2 series, between the lateral abdominal plates. Preanal plate large, single or double, bordered anteriorly by one or two plates. First anal-fin pterygiophore exposed in front of anal-fin as small, plate-like bone supporting odontodes. Total vertebrae 27, in one dissected specimen.

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 absent; single azygous plate at adipose-fin position in one cs specimen. Pectoral-fin rays I,6. Large spine slightly arched; tip of adpressed spine almost reaching or reaching to tip of pelvic fin. Pectoral-fin axillary slit present, with large slanted opening ventral to tip of posterior process of cleithrum. Pelvic-fin rays i,5, fin short, with tip of adpressed fin falling short of anal-fin origin in females, males so far unknown. Odontodes on ventral surface of thickened first pelvic-fin ray bent and oriented mesially. Anal-fin rays i,5. Caudal-fin rays i,14,i, with upper and lower unbranched rays subequal.

Color in alcohol. Dorsal portions of head and trunk light brown o pale yellow, cream to pale yellow ventrally. Two separate light marks from snout tip diverging towards nostrils. Compound pterotic and most of parieto-supraoccipial behind eyes brown. Posterior portion of parieto-supraoccipital lighter than surrounding areas, but not forming inverted Y-shaped mark. Trunk with five conspicuous dark brown bars; bar 1 merged with darkened predorsal area; bar 4 sometimes duplicated. Bars extending transversely from dorsal midline to ventral surface. Dark bars connected by zig-zag lateral dark stripe from compound pterotic to caudal-fin base. Ventral surface mostly unpigmented, but small concentrations of chromatophores on cheeks, lateral abdominal plates, and caudal peduncle. Bar 2 elongated ventrally to anal-fin origin; bars 3–4 reaching or almost reaching to ventral midline. Tooth cusps light yellow. Fins with transverse, brown bands formed by concentration of chromatophores on rays; bands more numerous on leading rays; membranes mostly hyaline. Dorsal fin without dark triangular spot at anterior portion of membrane, spine with 3–4 dark brown spots, branched rays with 2–3 dark bands. Pectoral-fin spine with 4–5 dark spots, branched rays with 2–3 irregular dark bands. Pelvic fin with 1–2 dark band. Anal fin with 1–2 indistinct dark bands. Caudal fin with dark transverse blotch at base and 2–3 irregular brown bands.

Sexual dimorphism. Males unknown for this species; all 14 specimens examined are females.

Geographical distribution. Rhinotocinclus loxochelis is known from creeks tributary to the rio Jamanxim, rio Tapajós basin, in the Jamanxim National Forest, Pará, Brazil ( Fig. 36 ).

Etymology. Rhinotocinclus loxochelis , from the Greek MQ p Q c (loxos), slanting, crosswise, and lfm ic (kelis), stain, spot, in allusion to the broken and oblique dark bars of the species. A noun in apposition.

Conservation status. The extinction risk of Rhinotocinclus loxochelis is assessed as low despite its restricted range. The species is known from three localities in the rio Jamanxim basin, with an Extension of Occurrence (EOO) estimated by the convex polygon of those localities of approximately 3,400 km 2. Both logging and gold mining are common in the region, but these threats are not believed to put the population in risk. Also, all three known localities are located inside the Jamanxim National Forest. For this reason, R. loxochelis 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 36 | Geographic distribution of Rhinotocinclus species of the R. bockmanni group in southeastern Amazon basin. Rhinotocinclus bockmanni (black dots); R. dani (red dots); R. hera (pink dots); R. loxochelis n. sp. (blue dots); R. marginalis n. sp. (white dots); R. pentakelis (yellow dots). T = Type-locality.

FIGURE 41 | Rhinotocinclus loxochelis, holotype, MPEG 38957, 22.6 mm SL, female, creek in Jamanxim National Forest, Itaituba, Pará, Brazil.