Ixinandria steinbachi (Regan, 1906)

Rodriguez, Mónica S., Cramer, Christian A., Bonatto, Sandro L. & Reis, Roberto E., 2008, Taxonomy of Ixinandria Isbrücker & Nijssen (Loricariidae: Loricariinae) based on morphological and molecular data, Neotropical Ichthyology 6 (3), pp. 367-378 : 370-374

Ixinandria steinbachi (Regan, 1906)

Fig. 5

Loricaria steinbachi Regan, 1906: 97 . Type locality: Salta, Argentina. - Eigenmann, 1911: 414 (listed under subgenus Rhineloricaria ). - Pozzi, 1945: 275 (Jujuy). - Arratia et al., 1983: 54 and 82 (Jujuy; río Bermejo). -Arratia & Menu Marque, 1984: 517 (reference).

Loricaria (Rhineloricaria) steinbachi . - Gosline, 1945: 102 [listed]. - Gomes, 1947: 24 [reference]. - Ringuelet & Arámburu, 1962: 53 [ Argentina]. - Ringuelet et al., 1967: 411, 413 [description and distribution in Argentina].

Ixinandria steinbachi . - Isbrücker, 1979: 91, 113 [new combination, lectotype designation]. - Isbrücker, 1980: 103 [reference]. - Isbrücker, 1981a: VI,75 [reference, discussion]. - Isbrücker, 1981b: 89 [reference]. - López et al., 1987: 31 [listed, Argentina]. - Burgess, 1989: 417 [reference]. - Fernández, 1996: 22 [Ledesma, Jujuy and Rosario de Lerma, Salta]. - Monasterio de Gonzo et al., 1998: 133-139 [trophic ecology]. - Isbrücker, 2001: 29 [reference]. - Nieva et al., 2001: 85 [La Ciénaga, río Arias, río Juramento basin, Salta]. - Barros et al., 2001: 9 [density in the río Arenales, Salta]. - Monasterio de Gonzo, 2002: 11-18 [description and comparision of dentition of three loricariids]. - López et al., 2002: 7 & 60 [endemism in the Subtropical Potamic Axis ecoregion]. - López et al., 2003: 45 [listed]. - Ferraris, 2003: 336 [listed]. - Menni, 2004: 195, 198 [río Aguas Negras, Ledesma, Jujuy, and río Rosario at 48 km of Salta, habitat]. - Monasterio de Gonzo, 2003: 191-192 [distribution and redescription]. - Menni et al., 2005: 34, 38 [río Aguas Negras and río Juramento basin]. - López & Miquelarena, 2005: 530, 534 [Paranoplatensean distribution, endemism in western South America]. - Monasterio de Gonzo et al., 2005: 36-41 [abundance and detritivourous trophic habits in río Popayán, Parque Nacional el Rey, Salta]. - Monasterio de Gonzo et al., 2005: 26 [distribution, listed to río Bermejo, río Juramento and río Dorado del Valle]. - Liotta, 2006: 365 [distribution]. - Covain & Fisch-Müller, 2007: 31 [distribution, habitat, sexual dimorphism, and reproductive habits]. - Ferraris, 2007: 263 [listed, distribution, and remarks].

Canthopomus montebelloi Fowler, 1940: 55 , fig. 10 [NEW SYNONYM]. Type locality: Monte Bello, Tarija, Bolivia. - Böhlke, 1984: 123 [type catalog]. - Gosline, 1945: 83 [listed]. - Gosline, 1947: 108 [reference].

Ixinandria montebelloi . - Isbrücker, 1979: 87 [new combination]. - Isbrücker, 1980: 103 [reference]. - Isbrücker, 1981a: VI,75 [reference, discussion]. - Burgess, 1989: 417 [reference]. - Isbrücker, 2001: 29 [reference]. - Ferraris, 2003: 336 [reference]. - Armbruster, 2004: 46, 66 & 68 [phylogeny of family Loricariidae ]. - López & Miquelarena, 2005: 534 [endemism in western South America]. - Ferraris, 2007: 263 [listed, distribution].

Diagnosis. As for the genus

Description. Morphometric data in Table 1. Head and body strongly depressed. Trunk and caudal peduncle becoming more compressed caudally. Dorsal profile of body convex from snout to end of supraoccipital, straight or slightly convex from supraoccipital to dorsal-fin spine, straight from dorsal fin to one or two plates before caudal fin. Upper edge of orbit not raised. Scarcely developed triangular postorbital notch.

Outline of head rounded in dorsal view. Head strongly flattened in mature males. Paired anterior postrostral and cheek plates scarcely developed ventrally. Odontodes curved, conical, and pointed, densely covering head, trunk, and fin rays, making fish somewhat hispid. Body odontodes scarcely distributed and grouped centrally in plates ( Fig. 6). Thick skin sometimes covering plates partially, hiding plate limits and covering odontodes. Snout tip with big globular protuber- ance of naked skin. This roundish naked area not reaching most anterior pore of infra-orbital ramus of sensory canal. Gill opening small. Mouth big and roundish. Lower lip margin with short digitiform papillae. Upper lip well developed, folded inwards with row of globular papillae. Big globular papillae arranged in regular rows on surface of lips. Numerous small globular papillae on mouth roof, bigger posteriorly. Maxillary barbel very small, mostly coalesced with lower lip. Teeth bilobed, with wide cusps, mesial more developed and slightly longer than lateral ( Fig. 7). Premaxilla with six to 18 (mean=12.4, n=71) teeth in functional series. Dentary with six to 15 (mean=10.3, n=46) teeth in functional series.

Abdomen completely naked, except for lateral abdominal plates. Preanal plate absent. Two to 11 (mean= 7.0, n= 72) lateral abdominal plates on each side. 27 to 32 (mean=29.4, n=72) plates in median lateral series, with well developed keels formed by hypertrophied odontodes. Five lateral series, sometimes broken and appearing to have six or seven lateral series; only posterior portion of median and midventral series with keels. Keels coalesced in last seven to 12 rings (mean=9.5, n=72). Middorsal series with 5-10 plates (mean=7.8, n=9) (better visible in cleared and stained material). Entire body with thick skin between the plates, especially in the lateral series. Predorsal plates usually arranged in irregular pattern, not forming rows. Supraoccipital and predorsal plates without keels. Transversal diameter of nasal capsule equal or slightly larger than eye diameter including notch (better visible in cleared and stained material).

Posterior margin of dorsal fin straight or slightly rounded, generally with first or second branched ray longest. Tip of dorsal fin, when depressed, reaching third or fourth (exceptionally fifth) plate posterior to fin insertion. Dorsal-fin spinelet absent. Posterior margin of pectoral fin convex, first or second branched ray longest, reaching to or slightly beyond pelvic-fin origin. Posterior margin of pelvic fin rounded; first or second branched ray longest, reaching to or falling slightly short of anal-fin origin. Posterior margin of anal fin rounded, with longest first or second (rarely) branched ray. Tip of anal fin, when depressed, reaching fifth or sixth plate posterior to fin insertion; three or four ventral plates along its base. Posterior margin of caudal fin truncated or slightly concave. Upper and lower unbranched rays never extending as filament. Two or three supracaudal plates covering base of caudal-fin rays, median plate sometimes absent.

Color in alcohol. Background color of dorsal surface of head and body dark brown with five darker transverse bars; first one inconspicuous on supraoccipital, others distributed between origin of dorsal fin and caudal fin. Last three bars sometimes continuing across ventral surface and forming dark brown rings. Some specimens with black spots on head and snout. Dorsal fin with dark gray circular spots. Pectoral and pelvic fins yellowish with dark circular spots. Sensorial pores on head and beginning of lateral canal pigmented with black. Ventral surface of body light brown in naked regions. Anal and caudal fins with dark dots arranged in bars on branched and unbranched rays. Ventral plates darkened around anal-fin base.

Color in life. Background color of head and body light brown with five dark brown transverse bars distributed as described above. Other markings as described above ( Fig. 8).

Sexual dimorphism. Males with head wide and flattened; long hypertrophied odontodes on sides of head and on upper side of branched pectoral-fin rays; short odontodes on remaining of dorsal surface of body, especially on predorsal region; unbranched pectoral-fin ray hypertrophied. Papillae in mouth cavity more numerous in males than in females. Outer margin of tooth cusps straight in females, rounded in males ( Fig. 7).

Ontogeny. Many structures vary ontogenetically in Ixinandria steinbachi . The premaxilla, dentary, and the pectoral girdle are ossified in a specimen of 17.2 mm SL, the smallest individual we were able to examine.At that size the pelvic girdle was not developed, the lateral abdominal plates and plates on the head and predorsal region were not formed. The lateral series of plates were represented by small platelets with one or two odontodes each.

In a specimen of 28.2 mm SL the pelvic girdle, the lateral connecting bone, the nucal plate, and the neurocranium are totally ossified. The plates on the head are represented by scarce odontodes and the lateral series of plates are almost entirely formed from the posterior region to level of the dorsal fin. Three small lateral abdominal plates are forming laterally on the abdomen, with one or few odontodes each.

Distribution and habitat. Upper río Juramento basin, río Salado drainage in Salta ( Argentina), upper río Bermejo in northwestern Argentina and southern Bolivia, and upper río Pilcomayo in southern Bolivia ( Fig. 9). Its presence in the río Pilcomayo is herein reported for the first time. Ixinandria steinbachi was caught in fast flowing waters between 15 and 65 cm depth, especially in places with filamentous algae, in mountainous areas at altitudes ranging from around 200 to 2900 meters a.s.l.. The minimun altitude where it was recorded is 210 m a.s.l. in the río Rosario, 48 km from the city of Salta. This species lives in fast flowing and highly oxygenated waters, with stony bottom, usually hiding under the stones during the day. Under 2200 m a.s.l. one species of Hypostomus , Heptapterus mustelinus , and some characids and other loricarids were found occurring syntopically with I. steinbachi ( Menni, 2004) .