Leptotocinclus ctenistus, Delapieve & A. & Reis, 2017

Delapieve, Maria Laura S., A., Pablo Lehmann & Reis, Roberto E., 2017, An appraisal of the phylogenetic relationships of Hypoptopomatini cascudinhos with description of two new genera and three new species (Siluriformes: Loricariidae), Neotropical Ichthyology 15 (4), No. e 170079, pp. 1-38 : 24-27

Leptotocinclus ctenistus , new species

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Fig. 15

Fig. 15. Leptotocinclus ctenistus, INPA 53272, holotype, male, 26.5 mm SL, Brazil, Amazonas , Maraã, igarapé São Sebastião,

tributary to igarapé do Baré, lago Amanã basin (02°17’06”S 64°40’36”W).

Holotype. INPA 53272 , male, 26.5mm SL, Brazil, Amazonas , Maraã , igarapé São Sebastião , tributary to igarapé do Baré, lago Amanã basin, 02°17’06”S 64°40’36”W, 17 January 2010, H. Lazzarotto & J. Oliveira.

Paratypes. Brazil, rio Amazonas basin: INPA 33985 , 7 , 19.1 -29.0 mm SL, and MCP 51457, 2 , 24.9-25.2 mm SL + 2 c&s, 24.3-26.7 mm SL, same data as holotype. INPA 33982 , 14 , 22.5-29.3 mm SL, and MCP 51458, 4 , 25.0- 26.4 mm SL + 2 c&s 23.3-26.5 mm SL, igarapé Solimõezinho , tributary to rio Unini , Barcelos , Amazonas , 01°30’18”S 62°58’15”W, 27 January 2010, H. Lazzarotto. INPA 34001 , 8 , 22.7-27.1 mm SL + 2 c&s 25.7-26.1 mm SL, and MCP 51459, 5 , 23.3-26.9 mm SL, igarapé do Solimõezinho, rio Unini basin, Barcelos, Amazonas, 01°30’17.7”S 62°58’15”W, 27 January 2010, H. Lazzarotto. MPEG 16620 , 1 , 27.7 mm SL, igarapé Tamanduá, tributary to rio Coari , Coari, Amazonas, 04°53’04.9”S 65°13’34.5”W, 18 December 2008, L. Montag. MPEG 16621 , 1 , 27.3 mm SL, and MPEG 16622 , 3 , 25.7-29.9 mm SL, igarapé Marta, tributary to rio Coari , Coari, Amazonas, 04°51’39.2”S 65°04’40.4”W, 29 July 2008, W. Wosiacki. MPEG 16623 , 1 , 25.8 mm SL, igarapé Onça, tributary to rio Coari, Coari, Amazonas, 04°52’08.7”S 65°18’03.7”W, 14 December 2008, L. Montag. MPEG 16624 , 1 , 29.6 mm SL, igarapé Tartaruga, tributary to rio Coari, Coari, Amazonas, 04°53’04.3”S 65°20’06.5”W, 15 December 2008, L. Montag . Colombia, rioAmazonas basin: ICNMHN 10054, 1, 22.5 mm SL, quebrada Tacana , tributary to río Amazonas at km 6.5 of road from Leticia to Tarapacá , Departamento Amazonas , 04°09’15”S 69°56’09”W, 30 June 2002, C. A. Pinto. ICNMHN 10093, 2, 17.4-18.9 mm SL, quebrada Tacana, tributary to río Amazonas at km 6.5 of road from Leticia to Tarapacá, Departamento Amazonas, 04°09’15”S 69°56’09”W, 19 July 2002, C. A. Pinto. ICNMHN 10123, 8, 14.8-28.4 mm SL, and MCP 51460, 3 , 20.9-25.1 mm SL + 1 c&s 19.8 mm SL, quebrada Tacana, tributary to río Amazonas at km 6.5 of road from Leticia to Tarapacá, Departamento Amazonas, 04°09’15”S 69°56’09”W, 30 May 2002, C. A. Pinto. ICNMHN 10286, 5, 26.1-30.6 mm SL, and MCP 51461, 2 , 28.2-29.1 mm SL + 2 c&s, 27.5- 31.4 mm SL, quebrada Tacana, tributary to río Amazonas at km 6.5 of road from Leticia to Tarapacá, Departamento Amazonas, 04°09’15”S 69°56’09”W, 12 January 2002, C. A. Pinto. ICNMHN 10327, 5, 24.9-30.1 mm SL, quebrada Tacana, tributary to río Amazonas at km 6.5 of road from Leticia to Tarapacá, Departamento Amazonas, 04°09’15”S 69°56’09”W, 10 December 2002, C. A. Pinto. ICNMHN 10348, 7, 18.7-27.6 mm SL, quebrada Tacana, tributary to río Amazonas at km 6.5 of road from Leticia to Tarapacá, Departamento Amazonas, 04°09’15”S 69°56’09”W, 17 July 2002, C. A. Pinto .

Diagnosis. Leptotocinclus ctenistus is distinguished from its only congener by median series of abdominal plates, present and arranged in one single row (vs. median series of abdominal plates absent); and by 3-6 lateral abdominal plates (vs. 1-2, but one specimen with 3). Additionally, Leptotocinclus ctenistus is distinguished by larger size of preanal plate (7.0-12.0% SL, Fig. 7f vs. 1.5-6.4% SL, Fig. 7e).

Description. Proportional measurements and counts in Tabs. 1-2. Body relatively small and slender, moderately elongated; head moderatly depressed. Dorsal profile of head and body slightly convex from snout tip to dorsal-fin origin; parietosupraoccipital slightly elevated leaving interorbital region convex. Trunk profile descending from dorsal-fin origin to anteriormost procurrent caudal-fin ray. Body deepest at dorsal-fin origin; body shallowest at posterior portion of caudal peduncle. Body ovoid to transversely depressed in cross section, progressively compressed posterior to anal-fin base. Greatest body width at cleithrum.

Anterior margin of snout broadly rounded in dorsal view. Snout with slight depression anterior to each nostril. Eye large, laterally positioned, barely visible in ventral view; iris operculum absent. Compound pterotic perforate only laterally, fenestrae increasing in size towards posterolateral margin of bone. Pore between canal-bearing cheek plate and fourth infraorbital present. Three predorsal plates anterior to trapezoidal nuchal plate. Odontodes on dorsal margin of snout slightly larger than other odontodes on head. Odontodes on ventral margin of snout distinctly enlarged. Posterior tip of parieto-supraoccipital without small tuft of enlarged odontodes even in specimens smaller than 20 mm SL. No other crests of odontodes on dorsal surface of head. Lips rounded and covered with globular papillae. Teeth slender, bifid, with blade-like larger medial cusp and smaller lateral cusp. Plates anterior to cleithrum absent.

Median series of lateral plates complete with lateral line continuous. Odontodes on head and trunk pointed, uniform in size and shape and conspicuously aligned; odontodes on caudal peduncle slightly larger. Odontodes on ventral surface of body smaller and evenly distributed, not arranged in lines. Body almost entirely covered by plates, except area around anus, region overlying lateral opening of swimbladder capsule, area between lower lip and pectoral girdle, and area around fin bases. Ventral portions of cleithrum and coracoid completely exposed and supporting odontodes. Abdomen covered by 3-6 (mean 4) elongate lateral abdominal plates and single series of 4-8 polygonal to roughly square middle abdominal plates. Single, large preanal plate between the pelvic fins. Anal tube and male urogenital papilla slightly right turned. Total vertebrae 27; ribs 6, beginning on eighth vertebral centrum, in addition to large rib on sixth centrum.

Dorsal fin I,7, its origin at vertical through middle of pelvic fin. Dorsal-fin spinelet absent. Pectoral fin I,6, with small axillary slit in skin behind fin insertion. Serrae absent along mesial margin of pectoral-fin spine. Pectoral fin reaching to vertical through midpoint of pelvic-fin unbranched ray. Adipose fin absent. Pelvic fin i,5, short, with robust thickened first ray shorter than two first branched rays. Skin flap absent on first unbranched pelvic-fin ray of males. Dorsal surface of first and sometimes second pelvic-fin branched rays with contact organ composed of row of enlarged odontodes. Anal fin i,5; first anal-fin pterygiophore exposed in front of unbranched fin ray. Odontodes on pelvic-fin unbranched ray turned and strongly pointing mesially. Caudal fin i,12,i (two specimens with i,11,i), forked, upper and lower lobes equal.

Color in alcohol. Ground color of dorsal surface of head and body tan to medium brown. Dark brown melanophores on head more densely concentrated on compound pterotic, parieto-supraoccipital, frontals, postrostral plates, anterior surface of upper lip, and posterior and mesial portions of naris flap. Melanophores on body concentrated on skin covering swimbladder opening, predorsal area, and on lateral stripe. Longitudinal dark brown lateral stripe on midlateral surface of head and body; stripe beginning laterally on snout tip partially covering ventral half of eye and continuing to end of caudal peduncle. Light brown melanophores roughly arranged in four dorsal blotches; one anterior to dorsal fin, one on posterior portion of dorsal fin, two at caudal peduncle. Posteriormost plates of both dorsal and ventral series of lateral plates less pigmented. Ventral surface of body mostly unpigmented except for ventral portion of snout plates, canal-bearing cheek plate, lateral region of pectoral girdle, lateral portions of lateral abdominal plates, and lateral portions of caudal peduncle. Dorsal and pectoral fins with 5-6 dark brown spots, continued as irregular bands on branched rays. Pelvic fin with 3-4 and anal fin with 2 such spots. Caudal fin with trapezoidal dark brown spot at base and 3-4 bands of brown melanophores on unbranched and branched rays. Interradial membrane of all fins unpigmented.

Sexual dimorphism. Males with a conical urogenital papilla behind the anal tube. Mature males also possess a pelvic-fin contact organ, composed of a row of enlarged odontodes on the dorsal surface of the first, sometimes second, pelvic-fin branched rays ( Fig. 13). Those odontodes are almost three times the size of other odontodes on the dorsal surface of the pelvic fin.

Distribution and habitat. Leptotocinclus ctenistus is known from tributaries to the rio Solimões and rio Negro in Brazil and Colombia ( Fig. 16). Collecting localities are blackwater creeks and small rivers. The Quebrada Tacana is a blackwater creek with a sandy bottom and the collecting station is located on the Terra Firme, above the level of the yearly seasonal flood ( Galvis et al., 2006).

Etymology. The specific name ctenistus from the Greek ktenistus, meaning combed, derived from ktenos, comb, in reference to the contact organ formed by a comb of odontodes on the pelvic fin of mature males. An adjective.

Conservation status. Leptotocinclus ctenistus is relatively frequent and abundant in the tributaries of the rio Solimões and rio Negro, with an EOO of approximately 128,000 km 2. As it is widespread and no eminent threats are detected, L. ctenistus can be categorized as Least Concern (LC) according to the International Union for Conservation of Nature (IUCN) categories and criteria ( IUCN Standards and Petitions Subcommittee, 2016).

Multivariate comparison. General morphological differences between Leptotocinclus ctenistus and L. madeirae were investigated using a Principal Components Analysis. The resulting first principal component included an expressive proportion of the total variance (57.3%), but all variable loadings were positive and varied little in magnitude, suggesting that it represents a general size factor. Plots of factor scores of principal component 2 vs. 3 grouped specimens into two slightly overlapping clusters ( Fig. 17). PC2 and PC3 included 17.3% and 7.0% of the total variance, respectively. Measurements with heavier loadings on PC2 were pectoral-pelvic fin distance (0.29), postdorsal length (0.20), caudal-peduncle width (-0.45), and naris diameter (-0.65); on PC3 heavier loadings were dorsal-fin base length (0.34), caudal-peduncle width (0.37), naris diameter (-0.27), and suborbital depth (-0.60). This difference in general morphospace indicates a slight body shape difference, difficult to detect with linear measurements, but supportive of the lineage independence hypothesis between Leptotocinclus ctenistus and L. madeirae .