Hisonotus aky Reis & Carvalho (2007: 84) 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 Carvalho, Tiago P. Reis, Roberto E. Zootaxa 2009 2009-05-20 2113 1 1 40 3M4VM [151,327,1234,1260] Actinopterygii Loricariidae Hisonotus Animalia Siluriformes 3 4 Chordata species iota sp. nov.   Fig. 2, Table 1     Hisonotus akynon ( Azpelicueta, Casciotta, Almirón, Körber, 2004).-  Reis & Carvalho (2007: 84)[listed].     Holotype: MCP42575, 33.4mm SL, female, Brazil, Santa Catarina, Coronel de Freitas, rio Chapecóat vila São Miguelon road from Coronel de Freitasto 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–  27.7mm SL; MCP 40029, 18+ 3 c&s, 21.6–29.7 mm SL, collected with the holotype.   Diagnosis.  Hisonotus iotadiffers 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 hungyby 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.   TABLE 1.Morphometrics and meristics of  Hisonotus iota. SD = Standard deviation, n = number of specimens, H = holotype.    types  H n Low High Mean SD  Standard length (mm) 33.4 20 22.6 33.4 26.8 -  Percent of Standard Length  Head length 37.2 20 36.3 41.1 38.4 1.15  Predorsal Length 50.4 20 47.5 52.6 50.1 1.24  Dorsal-fin spine length 21.9 20 21.9 27.0 24.8 1.20  Anal-fin unbranched ray length 13.1 20 13.1 19.3 16.9 1.29  Pectoral-fin spine length 22.5 20 22.5 29.5 27.4 1.65  Pelvic-fin unbranched ray length 16.6 20 15.9 21.5 18.8 1.67  Cleithral width 28.4 20 27.6 30.5 29.1 0.9  Thoracic length 18.8 20 16.0 19.3 17.8 0.87  Abdominal length 21.4 20 19.2 21.9 20.5 0.78  Body depth at dorsal-fin origin 21.7 20 19.9 23.7 22,3 0.78  Caudal-peduncle length 29.3 20 28.4 32.4 30.6 1.19  Caudal-peduncle depth 13.9 20 12.9 15.8 14.2 0.67  Percent of Head Length  Snout Length 51.3 20 48.6 53.8 51.3 1.33  Orbital diameter 15.2 20 15.1 17.5 16.1 0.76  Interorbital width 36.8 20 36.4 40.5 37.9 1.01  Head depth 55.7 20 51.1 57.9 54.8 1.97  Suborbital depth 22.0 20 21.4 27.2 22.9 1.29  Mandibular ramus 7.3 20 6.6 9.2 8.2 0.68  Meristics  Left premaxillary teeth 10 14 9 13 11.1 1.14  Right premaxillary teeth 10 16 9 14 11.3 1.44  Left dentary teeth 11 19 9 13 10.8 1.03  Rigth dentary teeth - 17 9 12 10.6 1.09  Left lateral scutes 21 20 20 22 20.9 0.59  Rigth lateral scutes 20 20 20 22 20.7 0.59   FIGURE 2.Holotype of  Hisonotus iota, MCP42575, 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. 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.   FIGURE 3.Skull of  Hisonotusin dorsolateral view showing infraorbital canal. A—  Hisonotus iotaspecies, MCP 40029, 28.0 mm SL. B—  Hisonotus ringueleti, MCP11215, 37.2 mm SL. SP— sphenotic; io—Infraorbitals; CP—coumpound pterotic. Scale bar is 2 mm. 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.   FIGURE 4.Scanning electron micrograph of snout anterior rostral margin of  Hisonotus iota, MCP40029, 29.7 mm SL. A—anterior view of rostrum; B—magnification of medial portion. Hypurals 1–2 and 3–5 completely fused, without median notch on posterior margin of caudal-fin. Total vertebrae 25–26 (2 c&s).   FIGURE 5.Trunk plates of  Hisonotusspeciesin lateral view of left side. A—  H. iota, MCP40029, 23.3 mm SL. B—  H. leucophrys, MCP41354, 40.8 mm SL. C—  H. megaloplax, MCP31779, 41.3 mm SL. D—  H. montanus, MCP41459, 37.9 mm SL. Scale bar is 4 mm.  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.   FIGURE 6.Arrangement of abdominal plates of  Hisonotusspecies.Anterior portion toward top. A—  H. iota, MCP40029, 28.0 mm SL. B—  H. leucophrys, MCP41354, 40.8 mm SL. C—  H. megaloplax, MCP31779, 37.8 mm SL. D—  H. montanus, MCP41459, 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.   TABLE 2.Frequency distribution for left and right lateral plate counts of species of  Hisonotusin the rio Uruguay basin. N = number of specimens.    Left Lateral Plates  Species 20 21 22 23 24 25 N Mean    H. nigricauda 7 31 22 60 23.3    H. ringueleti 4 34 29 67 23.4    H. aky 7 19 2 28 22.8    H. charrua 27 36 40 103 24.1    H. megaloplax 5 12 3 20 22.9    H. leucophrys 4 5 9 23.6    H. montanus 8 10 18 22.6    H. iota 5 13 2 20 20.9  continued.  Right Lateral Plates  Species 20 21 22 23 24 25 N Mean    H. nigricauda 6 33 21 60 23.3    H. ringueleti 5 30 32 67 23.4    H. aky 11 14 3 28 22.7    H. charrua 21 42 40 103 24.1    H. megaloplax 3 14 3 20 23.0    H. leucophrys 4 5 9 23.6    H. montanus 8 10 18 22.6    H. iota 8 11 1 20 20.7  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 iotais known only from the typelocality in rio Chapecó, a tributary of the upper rio Uruguaybasin ( 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  iotais from the Greek meaning anything very small, referring to the small size of the species compared to congeners. A noun in apposition. MCP 42575 2006-01-23 MCP, V de Freitas & C. A. S. Lucena & A. Bertaco & E. H. L. Pereira & J. F. P. Silva. Brazil Coronel de Freitas -26.857224 Sao Miguel 20 -52.74139 rio Chapeco 3 4 33.4 1 Santa Catarina holotype [197,609,1533,1559] ANSP 3 4 ANSP 187472, 4, 26.5 1 paratype [624,851,1533,1559] MCP 3 4 27.7 1 paratype MCP 3 4 18 1 holotype