Hisonotus aky (Azpelicueta, Casciotta, Almiron & Korber, 2004) , MCP, 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 : 26-28

Hisonotus aky , new combination

( Azpelicueta, Casciotta, Almirón & Körber, 2004).

( Figures 15 , Table 6)

Epactionotus aky Azpelicueta, Casciotta, Almirón & Körber, 2004: 81–90 , [original description, type locality: Arroyo Garibaldi, rio Uruguay basin at Missiones, Argentina].- Liotta, 2005:354 [listed].

Hisonotus sp. “ Argentinien ”.- Evers & Seidel, 2002 [listed and illustrated].

Material examined. All from rio Uruguay basin: AI 124, holotype of Epactionotus aky , 29.2 mm SL, Argentina, Missiones, Arroyo Garibaldi, tributary of Arroyo Yabotí-Guazú, 26°38’46”S 053°59’55”W . AI 125, paratypes of E. aky , 7, 25.0–34.5 mm SL, same collecting data as holotype. MCP 41474, 36 + 3 c&s 18.2–39.7 mm SL, Brazil, Rio Grande do Sul, Paim Filho, rio Forquilha at Espraiado bathing spot on secundary road from Maximiliano de Almeida to Paim Filho, 27°40’37”S 51°44’11”W .

Diagnosis. Hisonotus aky differs from its congeners, except from H. iota , and H. montanus by having an infraorbital canal entering the infraorbital series via the compound pterotic vs. infraorbital canal entering the infraorbital series via the sphenotic. Hisonotus aky differs from H. iota by the presence of a narrow odontodefree band in the anterior portion of snout ( Fig. 16 ); and by having 27–29 vertebrae vs. presence of a snout completely covered with odontodes, and 25–26 vertebrae. Hisonotus aky differs from H. montanus by having narrow longitudinal light stripes on head; and by the absence of white marks on the dorsal surface of head vs. wider longitudinal light stripes markings on the head; and presence of white marks on dorsal surface of head.

Distribution and habitat. Hisonotus aky is known only from two tributaries to the rio Uruguay widely separated from each other, the Arroyo Yabotí-Guazú a tributary to middle Río Uruguay basin in Argentina (type-locality), and the rio Forquilha a tributary to upper rio Uruguay basin in Brazil ( Fig. 8 ). There is a large distributional hiatus between these populations located in different tributaries. However, these populations are similar in morphometric data ( Tab. 6) and no additional morphological difference was found, except for a more densely pigmented caudal fin in the specimens from rio Forquilha. Hence, these populations are considered conspecific. The population in rio Forquilha inhabits a rapid flowing watercourse, with clear to brown waters and rocky bottom. The individuals were found between aquatic vegetation mainly composed of Echinodorus sp. , which form green islands attached to a rocky substrate.

Remarks. Hisonotus aky ( Azpelicueta, Casciotta, Almirón & Körber, 2004) was originally described in Epactionotus Reis & Schaefer, 1998 because of its supposed possession of three synapomorphies of that genus: absence of an expanded fleshy flap on the dorsal surface of the first pelvic-fin ray in males, neural spine of seventh vertebra not contacting the nuchal plate dorsally (contacting unpaired predorsal plates), and first dorsal proximal radial contacting the eighth vertebral centrum. However, the examination of type specimens of Epactionotus aky indicated the absence of most diagnostic features of Epactionotus . The first pelvic-fin ray without a dorsal skin flap in males is a derived feature that independently evolved three times in the Hypoptopomatinae ( Schizolecis , Epactionotus , and the clade formed by Acestridium , Oxyropsis , Hypoptopoma , and Nannoptopoma ), according to the topology proposed by Schaefer (1998:382) and Gauger & Buckup (2005:511). The presence of a fleshy flap on the dorsal surface of the first pelvic-fin ray of mature males is plesiomorphic and shared by all species of Hisonotus , most hypoptopomatines, and Epactionotus aky ( Fig 17 ). The character-states: neural spine of seventh vertebra not contacting the nuchal plate dorsally, and the first proximal radial of dorsal fin contacting the eighth vertebra ( Fig. 18A ), are not present in H. aky . Hisonotus aky shares with rem aining Hisonotus species and other hypoptopomatines (except Microlepidogaster ) the neural spine of the seventh vertebra contacting the nuchal plate, at least posteriorly, and the first proximal radial of dorsal fin contacting the seventh vertebra ( Fig. 18B ). Another character, discussed by Azpelicueta et al. (2004), suggesting the inclusion of H. aky in Epactionotus is the presence of light longitudinal stripes on head and trunk. Because the presence of light stripes is more widespread among hypoptopomatines and appears in several species of Hisonotus , that feature does not diagnose H. aky as belonging to the genus Epactionotus . Moreover, Epactionotus aky shares with two species of Hisonotus ( H. iota and H. montanus ) the presence of an infraorbital canal entering the infraorbital series via the compound pterotic, which is a derived feature and suggests a close relationship between these three species. For these reasons, Epactionotus aky is here transferred to the genus Hisonotus .

Figures

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).

FIGURE 15. Hisonotus aky, MCP 41474, female, 33.7 mm SL. Rio Forquilha at Espraiado bathing spot on secondary road from Maximiliano de Almeida to Paim Filho, Paim Filho, Rio Grande do Sul, Brazil.

FIGURE 16. Scanning electron micrograph of snout anterior rostral margin of Hisonotus aky, MCP 41474, 34.7 mm SL. A—anterior view of rostrum; B—magnification of medial portion.

FIGURE 17. Paratype of Hisonotus aky, AI 125, male, 34.5 mm SL. Anterior portion of body in ventrolateral view. Arrow indicates the developed fleshy flap on pelvic-fin unbranched ray of adult male.

FIGURE 18. Anterior portion of axial skeleton in lateral view. A— Epactionotus bilineatus, MCP 29293, 36.5 mm SL, neural spine of seventh vertebra not contacting nuchal plate dorsally, and first proximal radial of dorsal fin contacting eighth vertebra. B— Hisonotus aky, MCP 41474, 37.2 mm SL, neural spine of seventh vertebra contacting nuchal plate, and first proximal radial of dorsal fin contacting the seventh vertebra. FR = first proximal radial; NP = nuchal plate; V = vertebra. Scale bar is 5 mm.