Rogadius azizahae, a new flathead (Perciformes: Platycephalidae) from the South China Sea.

A new flathead Rogadius azizahae (Platycephalidae) is described on the basis of five specimens [102.5-107.8 mm standard length (SL)] collected off the east coast of the Malay Peninsula, southern South China Sea. The new species is morphologically similar to Rogadius mcgroutheri Imamura, 2007, known from the Coral Sea off eastern Australia and New Caledonia, the two species sharing most diagnostic characters, including a minute, weakly developed antrorse spine on the preopercle [vs. a long, stout antrorse spine present in Rogadius asper (Cuvier in Cuvier & Valenciennes, 1829), Rogadius fehlmanni Knapp, 2012, and Rogadius pristiger (Cuvier in Cuvier & Valenciennes, 1829)]; usually a single preocular spine [vs. 2-4 in R. fehlmanni and 2-5 in Rogadius welanderi (Schultz in Schultz et al., 1966)]; no accessory spines along the preocular spine base [vs. present in R. fehlmanni and Rogadius serratus (Cuvier in Cuvier & Valenciennes, 1829)]; and no longitudinal black band on the caudal fin (vs. present in Rogadius patriciae Knapp, 1987). The new species can also be distinguished from R. mcgroutheri by having 11 dorsal-fin soft rays [vs. 11 or 12, modally 12 (25 of 30 specimens) in the latter]; 7 lower gill rakers [vs. 5-7, modally 6 (21 of 30)]; the caudal fin brown basally, broadly whitish (semitranslucent) anteriorly and almost entirely brown on the posterior half (vs. ca. 4 irregular variously sized vertical rows of black blotches); the pelvic fin with ca. 6-8 rows of narrow, wavy black bands or dotted lines (vs. largely brownish, with no defined bands or spots); a relatively large orbit, its diameter 12.4-12.8 (mean 12.6)% SL [vs. 11.4-12.3 (11.7)% SL in 100-110 mm SL specimens]; and relatively narrow interorbital region, its width 1.3-1.5 (mean 1.4)% SL [vs. 1.7-2.2 (1.9)% SL]. DNA barcoding also indicated distinct divergence (14.3-14.4% uncorrected p-distance) between the new species and R. mcgroutheri. A revised key to species of Rogadius is provided.