bra (21st). Pelvic fin inserted anterior to vertical through dorsal-fin origin, not covering urogenital opening. Pelvic-fin rays i,4 (i,4); third and fourth rays longest; contralateral medial rays not overlapping in relaxed fins. Caudal fin with i,5 rays on upper hypural plate and i,6–7 rays on lower hypural plate (Fig 3) (i,6) with distal margin straight to slightly rounded. Smaller specimens (less than 67.3 mm SL) with anteriormost three caudal-fin rays of upper hypural plate slightly longer. Upper caudal plate with hypurals 4 and 5 fused together and hypural 3 autogenous; lower caudal plate with parahypural, hypurals 1 and 2 fused (Fig 3). Procurrent caudal-fin rays thickly ossified and rigid; 31–35 dorsally (holotype 34) and 13 ventrally (13) (Fig 3). Dorsal procurrent caudal-fin rays extending over tips of thirteen neural spines (13) and ventral procurrent caudal-fin rays extending dorsal to tips of five to six hemal spines (Fig 3) (holotype six). Vertebrae 37–38 (38). Ribs 11–12 pairs (11); first to sixth rib thicker.
Color in alcohol.
Sides and dorsal surface of body and head with marbeled color pattern composed of black blotches irregular in shape and size, overlapped by superficial layer of small and less pigmented spots over pale yellow background, forming marbled color pattern (Fig 1). Blotches of dorsal surface of body and head larger, becoming smaller towards to ventrolateral region. Ventral surface of head and anteriormost portion of trunk pale yellow. Ventral surface of caudal peduncle region with inconspicuous and faint black blotches. Barbels with scattered black blotches dorsally and pale yellow ventrally. Opercular and interopercular patches of odontodes pale yellow. Pectoral, dorsal and anal fins with black blotches in proximal portion and whitish band distally. Pelvic fin hyaline with few inconspicuous black blotches. Caudal fin with black blotches in proximal portion becoming inconspicuous towards distal margin.
Color in life.
Overall coloration of specimens in life similar to specimens after fixation with exception of brighter yellow background and distal portions of fins hyaline (Fig 2).
The Tabay stream basin through 192 km from its headwaters at Campo Viera to its mouth on the Paraná River, at Jardín América (Fig 4). The stream bed is mainly composed of basaltic bedrock, in which sections with waterfalls and pools alternates all along its run. At the type locality (Tabay waterfall; Fig 5), the stream is surrounded by remnants of the Paranaense riparian forest, with its left margin degraded due to a camping site. This waterfall consists of three consecutive falls, the main one is 10m high and 20–50m wide, which drains into a narrow gorge. All specimens of Trichomycterus ytororo were captured above the waterfalls at shallow areas (about 1 meter depth or less) or in rapids witha predominantly rocky bottom and strong current. Trichomycterus davisi was the single congener recorded at the type locality, which was not collected syntopically with T. ytororo.
Stars represent the type localities. Some triangles symbols represent more than one collection locality. Numbers 1, 2, 3 indicate the Paraguay, Paraná and Iguazú Rivers, respectively.
Trichomycterus ytororo is so far known only from its type locality, the Tabay waterfalls in the Tabay stream (Fig 5), a tributary of the left bank of the Paraná River, province of Misiones, northeast of Argentina (Fig 4).
The new species proposed herein is allocated in the genus Trichomycterus (subfamily Trichomycterinae) due to the presence of all the synapomorphies for the clade that includes all the trichomycterids excepting the Copionodontinae and Trichogeninae and lacks those derived characters that support the clade comprising the subfamilies Glanapteryginae, Sarcoglanidinae, Stegophilinae, Tridentinae, and Vandelliinae . The presence of the levator internus 4 muscle originating from the neurocranial floor and the dorsal face of the posttemporo-supracleithrum, a synapomorphy for Trichomycterinae latu sensu , in the new taxon also supports its inclusion in the sub