Hisonotus iota, Carvalho, Tiago P. & Reis, Roberto E., 2009

Carvalho, Tiago P. & Reis, Roberto E., 2009, Four new species of Hisonotus (Siluriformes: Loricariidae) from the upper rio Uruguay, southeastern South America, with a review of the genus in the rio Uruguay basin, Zootaxa 2113 (1), pp. 1-40 : 4-12

Hisonotus iota , new species

Fig. 2 , Table 1

Hisonotus aky non ( Azpelicueta, Casciotta, Almirón, Körber, 2004).- Reis & Carvalho (2007: 84) [listed].

Holotype: MCP 42575, 33.4 mm SL, female, Brazil, Santa Catarina, Coronel de Freitas, rio Chapecó at vila São Miguel on road from Coronel de Freitas to Quilombo , rio Uruguai basin, 26°51’26”S 052°44’29”W, 23 Jan 2006, C. A. S. Lucena, V. A. Bertaco, E. H. L. Pereira & J. F. P. Silva.

Paratypes. ANSP 187472 , 4 , 26.5 – 27.7 mm SL; MCP 40029, 18 + 3 c&s, 21.6–29.7 mm SL, collected with the holotype .

Diagnosis. Hisonotus iota differs from its congeners, except from Hisonotus hungy , by the lower lateral plate count 20–22 (mode 21) vs. 22–29 lateral plates ( Tab. 2), and by the lower vertebral count 25–26 vs. 27–32 vertebrae. It differs from Hisonotus hungy by having an infraorbital canal entering the infraorbital series via the compound pterotic ( Fig. 3A ) vs. infraorbital canal entering the infraorbital series via the sphenotic ( Fig. 3B ).

Description. Morphometrics and meristics in Table 1. Adult size small for members of this genus (maximum size 33.4 mm in SL). Body stocky, without conspicuous keels. Caudal peduncle round in cross section. Dorsal body profile almost straight from snout to parieto-supraoccipital tip, convex bump on internareal region. Almost straight from parieto-supraoccipital tip to dorsal-fin origin, except for posterodorsally inclined profile of nuchal region. Dorsal-fin base straight and posteroventrally sloped, straight from posterior end of dorsal-fin base to posterior end of caudal penduncle. Ventral profile straight from snout tip to anal-fin origin, concave at anal-fin base, and straight from posterior end of anal-fin base to caudal-fin origin. Greatest body depth at dorsal-fin origin. Least body depth at caudal peduncle. Posterior profile of caudal fin concave. Head and snout broad, snout rounded in dorsal view, body progressively narrowing posterior to pectoral-fin insertion. Snout region anterior of nares depressed, interorbital region slightly convex. Upper margin of orbit not elevate. Eye dorsolaterally positioned. Iris operculum present.

Pectoral fin I,6. Pectoral-fin posterior margin gently curved, when depressed tip extending anterior to middle of pelvic fin. Posterior margin of pectoral-fin spine smooth in adults, juveniles with feeble serrae along distal third of pectoral-fin spine. Pectoral-fin axillary slit present, slit posteroventrally sloped below posterior margin of cleithral process. Pelvic fin i,5, tip of depressed fin just reaching anal-fin origin in females, but extending far beyond that point in males. Dorsal fin II,7, its origin located posterior to vertical through pelvicfin origin. Dorsal-fin spinelet somewhat rounded in shape. Anal fin i,5. First anal-fin pterygiophore exposed anterior to anal fin. Adipose fin absent. Caudal fin i,14,i.

Body almost entirely covered by plates except for region overlying opening of swim bladder capsule, area between pectoral girdle and lower lip, region around anus, and area around base of paired fins. Rostral plate with posterior notch articulation with mesethmoid. Rostral plate thickened, anterior margin covered by odontodes without anterior odontode-free band ( Fig. 4 ). Region anterior to nares completely covered by plates, prenasal plates present and not reduced in size. Three rows of predorsal plates. Lateral plate series formed by 20–22 plates ( Tab. 2). Lateral line incomplete, with gap in line of pores along midlength of body, posterior portion of lateral line sometimes absent. Median-plate series truncated, not reaching posterior end of caudal peduncle ( Fig. 5A ). Lateral abdominal plates large and forming regular series of three to five plates on each side. Median abdominal series formed by one to three irregularly arranged series. Plates of pre-anal shield region large ( Fig. 6A ). Coracoid and cleithrum exposed and covered by odontodes, except for medial region of cleithrum between arrector fossae opening and symphysis.

Head without conspicuous crests, except for enlarged odontodes on parieto-supraoccipital tip, forming raised tuft ( Fig. 7 ). Head, fin rays, and body plates covered with odontodes, these larger on anterior surface of all fin spines, and on ventral margin of rostrum. Anteroventral margin of compound pterotic with median-tolarge size perforations. Infraorbital canal entering infraorbital series via compound pterotic. Lips roundish and papillose, posterior margin of lower lip gently fimbriate to smooth. Maxillary barbel present.

Premaxillary and dentary teeth bifid, slender proximally and flattened distally; major (medial) cusp large and rounded, minor (lateral) cusp minute and pointed. Accessory patch of teeth absent on dentary and premaxilla.

Hypurals 1–2 and 3–5 completely fused, without median notch on posterior margin of caudal-fin. Total vertebrae 25–26 (2 c&s).

Color. Ground color of dorsal and lateral surfaces carbon black. Dorsolateral region of head with paired longitudinal stripes, begining at tip of snout, passing through nares and reaching anterior orbit margin. Parieto-supraoccipital tip lighter than surrounding areas. Ventrolateral and ventral surfaces yellowish, with scattered chromatophores, most concentrated on cheek, bases of paired fins, and caudal peduncle. Fins mostly unpigmented, except for dark transverse bars, forming striped pattern. Middle portion of caudal fin with wide hyaline band. In life, ground color of dorsum and flanks dark green.

Sexual dimorphism. Characterized by the urogenital papilla, positioned just behind the anal opening in males. Adult males also possess a developed fleshy flap along the dorsal margin of the first thickened pelvicfin ray, that is absent in females. The flap is slightly wider basally and progressively narrows distally. Middle portion of first and second branched rays with a slightly developed fleshy flap. Flap is absent in juvenile males and females. Males have a longer pelvic-fin that extends beyond the anal-fin origin, with pelvic fin just reaching the origin of anal fin in females.

Distribution and habitat. Hisonotus iota is known only from the type locality in rio Chapecó, a tributary of the upper rio Uruguay basin ( Fig. 8 ). Rio Chapecó, at the collection site of the new species, is a wide and shallow river with a median to fast waterflow. The stream has clear waters running over a rocky bottom. The species was collected in the aquatic submersed vegetation.

Etymology. The species epithet iota is from the Greek meaning anything very small, referring to the small size of the species compared to congeners. A noun in apposition.

Figures

FIGURE 2. Holotype of Hisonotus iota, MCP 42575, female, 33.4 mm SL. Rio Chapecó at vila São Miguel on road from Coronel de Freitas to Quilombo, Coronel de Freitas, Santa Catarina, Brazil.

FIGURE 3. Skull of Hisonotus in dorsolateral view showing infraorbital canal. A—Hisonotus iota species, MCP 40029, 28.0 mm SL. B—Hisonotus ringueleti, MCP 11215, 37.2 mm SL. SP— sphenotic; io—Infraorbitals; CP—coumpound pterotic. Scale bar is 2 mm.

FIGURE 4. Scanning electron micrograph of snout anterior rostral margin of Hisonotus iota, MCP 40029, 29.7 mm SL. A—anterior view of rostrum; B—magnification of medial portion.

FIGURE 5. Trunk plates of Hisonotus species in lateral view of left side. A—H. iota, MCP 40029, 23.3 mm SL. B—H. leucophrys, MCP 41354, 40.8 mm SL. C—H. megaloplax, MCP 31779, 41.3 mm SL. D—H. montanus, MCP 41459, 37.9 mm SL. Scale bar is 4 mm.

FIGURE 6. Arrangement of abdominal plates of Hisonotus species. Anterior portion toward top. A—H. iota, MCP 40029, 28.0 mm SL. B—H. leucophrys, MCP 41354, 40.8 mm SL. C—H. megaloplax, MCP 31779, 37.8 mm SL. D—H. montanus, MCP 41459, 37.9 mm SL. Scale bar is 2 mm.

FIGURE 7. Scanning electron micrograph of predorsal region of Hisonotus iota, showing raised tuft of odontodes in posterior tip of parieto-supraoccipital. MCP 40029, 29.7 mm SL. Anterior portion toward top. A—dorsal view of predorsal region. B—magnification of raised odontodes. SOC—parieto-supraoccipital; PD—predorsal plates; NP—nuchal plate.

FIGURE 8. Drainage map showing distribution of Hisonotus species in the upper rio Uruguai basin. Some symbols represent more than one collecting locality. Open symbols represent type locality. Hisonotus iota (square); Hisonotus leucophrys (star); Hisonotus megaloplax (triangles); Hisonotus montanus (asterisk); and Hisonotus aky (circles).