Otothyropsis piribebuy, Calegari & A. & Reis, 2011

Calegari, Bárbara B., A., Pablo Lehmann & Reis, Roberto E., 2011, A new species of Otothyropsis (Siluriformes: Loricariidae) from the rio Paraguay basin, Paraguay, Neotropical Ichthyology 9 (2), pp. 253-260 : 255-258

Otothyropsis piribebuy , new species

Figs. 3-4

Undetermined genus LG2. -Evers & Seidel, 2005: 434 (locality: Paraguay, photographs, spawning).

Holotype. CZCEN 332, 28.8 mm SL, female, Paraguay, Departamento Cordillera, Eusebio Ayala, rio Piribebuy a tributary to the rio Manduvira, rio Paraguay basin, 25º22’09”S 56º58’20”W, 6 Jan 2008, H. S. Vera Alcaraz, J. J. Rasquin Centurion, M. C. Paradeda & G. Solalinde. Otothyropsis Ribeiro, Carvalho & Melo, 2005: 491 (Type species: O. marapoama Ribeiro, Carvalho & Melo, 2005: 491 , by original designation).

Diagnosis. Otothyropsis is diagnosed among the Hypoptopomatinae based on the following non-exclusive synapomorphies: elongated posterior extension of the compound pterotic, which forms de dorsal margin of an augmented lateral opening of the swimbladder capsule (char. 8, independently acquired by Otothyris and Pseudotothyris ), reduced upper pharyngeal tooth plate (char. 23), and middorsal series of lateral plates truncated before the caudal fin (char. 32). In addition, Otothyropsis can be distinguished from most other members of the Otothyrini (sensu Schaefer, 1998; except Parotocinclus , Hisonotus , Epactionotus , and New Taxon 3) by the possession of a notch on the postero-dorsal region of the rostral plate (char. 35) and by having enlarged odontodes on the ventral and dorsal margins of the snout (char. 39). Otothyropsis is further differentiated from Pseudotocinclus , Eurycheilichthys , Schizolecis , Otothyris , and Pseudotothyris by the possession of a single median rostral plate (char. 34).

Paratypes. ANSP 191484 , 5 , 19.7-25.3 mm SL, CZCEN 333 , 20 , 17.3-27.2 mm SL, MCP 44394, 25 , 16.7-28.3 mm SL, 3 c&s, 17.5- 27.6 mm SL, same data as holotype . MCP 45754, 2 , 25.4-25.7 mm SL, Paraguay, Departamento San Pedro, Lima, rio Aguaray at Lima , tributary to the rio Jejui , rio Paraguay basin, 23º52’35”S 56º29’01”W, 27 Dec 2007, H. S. Vera Alcaraz & P. Britez .

Diagnosis. Otothyropsis piribebuy is diagnosed from O. marapoama by having the middle series of lateral plates truncated two plates before the caudal fin (vs. truncated at least three plates before the caudal fin); the inner margin of the pectoral-fin spine smooth, with no serrae (vs. small serration on the distal portion of the pectoral-fin inner margin); the distal margin of the accessory flange of the first ceratobranchial pointed (vs. distal margin wide and rounded); the mid-dorsal lateral series with 17-18 plates and continuous, (vs. mid-dorsal lateral series with 10-11 plates and discontinuous with an intermediate gap of 3-5 plates); and the abdomen usually with unplated areas anteriorly in adults (vs. abdomen entirely covered with dermal plates in adults; Fig. 5 ). In addition to that, males of O. piribebuy are distinguished from males of O. marapoama by their longer preanal length (63.0-66.8% vs. 59.5-63.0% HL) and a smaller number of middle lateral plates (19-20 vs. 21-22).

Description. Proportional measurements and counts given in Tables 2 and 3, respectively. Dorsal body profile slightly arched from snout to origin of dorsal fin.

Slightly concave and postero-ventrally oriented along dorsal-fin base, straight from terminus of dorsal-fin base to end of caudal peduncle and angling upward slightly immediately before caudal-fin origin. Ventral body profile approximately straight, slightly ventrally oriented to pelvicfin origin and slightly postero-dorsally oriented from that point to end of anal-fin base. Greatest body depth at dorsalfin origin. Least body depth at posterior portion of caudal peduncle. Greatest body width along opercular and cleithral regions. Body progressively narrowing caudally from pelvicfin region. Caudal peduncle vertically oval in cross-section.

Head moderately broad, snout rounded in dorsal view. Region of prenasal plates between nostrils protuberant, bordered by elongate and deep depressions extending anterolaterally from each nostril to near snout tip. Eye small, dorsolaterally positioned. Iris operculum present. Dorsal margin of orbit slightly elevated. Compound pterotic perforate with middle to large size fenestrae, larger fenestrae on anteroventral portion.

Body entirely covered by dermal plates, except region around anus, region overlying lateral opening of swimbladder capsule, depression from nostril to rostral plates, area between pectoral girdle and lower lip, area around bases of paired fins, and scattered areas on anterior abdomen. Abdominal region covered with wide lateral abdominal plates laterally and with roundish to irregular, small platelets medially. Unplated areas usually present near the pectoral girdle and between lateral and medial patches of plates ( Fig. 5 ) - one male in MCP 44394 with abdomen fully covered with plates. Ventral portions of cleithrum and coracoid completely exposed and supporting odontodes. Dorsal body surface with one slightly developed keel from posterior orbital margin to terminus of posterior extension of compound pterotic. Three transverse rows of predorsal plates, including nuchal plate. Median series of lateral plates with 19-20 plates. Lateral line with intermediate gap of 3-4 plates without sensory canal; last 3 plates without canal. Mid-dorsal series of lateral plates long and continuous, with 17-18 plates, ending 2-3 plates before the last plate in middle series. Rostral plates well developed and projected ventrally under snout margin. Odontodes on head and trunk pointed, strongly curved, uniform in size and distribution and not arranged into distinct rows. Odontodes on head not forming ridges. Odontodes on dorsal and ventral margins of snout much larger than surrounding ones. Fin rays covered by odontodes, larger on leading margin of all fins. Lips rounded and papillose, with small maxillary barbel laterally. Lower lip small, its posterior border approximately on vertical line passing through anterior margin or middle of eye. Teeth slender, bifid, with blade-like larger medial cusp and smaller lateral cusp. Contiguous neural spines suturally articulated to each other from vertebral centrum to or almost to dorsal end in adults.

Dorsal-fin II,7, its origin at vertical running close pelvicfin origin. Spinelet reduced, rounded and plate-like, and dorsalfin locking mechanism not functional. Adipose fin absent. Pectoral fin I,6, with posterior margin straight to slightly rounded. Tip of depressed pectoral fin extending to approximately end of pelvic-fin thickened first ray. Axillary slit of pectoral fin present, moderate in size and located below the lateral cleithral process. Pelvic fin i,5, short, with robust thickened first ray; posterior margin distinctly rounded. Tip of adpressed fin extending to anal-fin origin in males; reaching to anus in females. Adult males with fleshy flap along posterodorsal margin of thickened first pelvic-fin ray. Anal fin i,5. Caudal fin i,14,i.

Color in alcohol. Ground color of dorsal surface of head and body light to median brown, darker laterally on flanks; mostly unpigmented ventrally, except for light brown caudal peduncle and ventral portion of cheek and rostral plates. One sinuous light stripe from snout tip to each nostril, continuing as thin line through upper margin of orbit and compound pterotic. Two inconspicuous lighter stripes on each side of predorsal region and flanking dorsal fin. Fin membranes hyaline with dark brown chromatophores arranged in irregular transverse bands on rays. Caudal fin with four or five transverse bands of dark pigmentation, both on rays and membrane, stronger on base and lower lobe, sometimes imperceptible on upper. Bands on caudal-fin sometimes merging to form mostly dark lower lobe. One irregularly shaped, unpigmented area on middle of two or three lowermost branched rays usually conspicuous.

Sexual dimorphism. Secondary sexual dimorphism in hypoptopomines is primarily characterized by the possession by males of an urogenital papilla, located immediately posterior to the anus, which is absent in females. Adult males also posses a fleshy flap along the dorsal margin of the thickened first pelvic-fin ray in most species, which is also absent in females. Otothyropsis piribebuy shares the two sexually dimorphic features above, and in addition has a longer first pelvic-fin ray, reaching to the origin of the anal fin (vs. shorter, never reaching to that point in females). Furthermore, O. piribebuy displays a remarkable secondary sexual dimorphism in the size of the naris opening, which is much bigger in males and affects most proportions of the head. Males have a smaller internareal distance (6.3-10.2 vs. 12.3-15.9% HL in females; Fig. 6 ), smaller prenasal length (28.9-32.9 vs. 31.6-36.4% HL in females), and larger orbital diameter (12.3-14.1 vs. 14.0-15.1% HL in females). Males also have a narrower body at the level of the dorsal-fin origin (16.2-19.8 vs. 19.5-22.7% SL in females).

Distribution and habitat. Otothyropsis piribebuy is known from two localities on the left tributaries to the río Paraguay, the río Piribebuy near Eusébio Ayala, Cordillera and the río Aguaray near Lima, San Pedro, Paraguay ( Fig. 7 ). In both localities the fishes were collected on marginal vegetation, mainly formed by hanging grasses in the former and floating water-hyacinths ( Eichornia ) is the later.

Etymology. Otothyropsis piribebuy is named after the rio Piribebuy, rio Paraguay basin, where most type specimens were collected. In the native Guarany language “Piri vevui” means gentle breeze, a sensation caused by the many cool rivers in the region. A noun in apposition.

Figures

Fig. 3. Otothyropsis piribebuy, holotype, CZCEN 332, 28.8 mm SL, female, Paraguay, Departamento Cordillera, Eusebio Ayala, río Piribebuy a tributary to the río Manduvira, río Paraguay basin.

Fig. 4. Life coloration of Otothyropsis piribebuy, female paratype, MCP 44394, 28.3 mm SL, Paraguay, Departamento Cordillera, Eusebio Ayala, rio Piribebuy a tributary to the rio Manduvira, rio Paraguay basin. Photo by Hector Vera Alcaraz.

Fig. 5. Dermal plates of abdominal region of Otothyropsis. a. O. piribebuy, MCP 44394, 26.9 mm SL. b. O. marapoama, MCP 42119, 30.8 mm SL. Lateral abdominal plates in gray and central abdominal plates stippled. Scale bar = 1 mm.

Fig. 6. Otothyropsis piribebuy, sexual dimorphism in the size of the nostrils. a. Female, paratype, MCP 44394, 24.4 mm SL. b. Male, paratype, MCP 44394, 26.9 mm SL. Scale bar = 1 mm.

Fig. 7. Geographic distribution of Otothyropsis marapoama (dots) and O. piribebuy (squares). Open symbols for type localities.