Two new species of the butterflyfish genus Roa (Perciformes: Chaetodontidae)

Two new species of Roa (Chaetodontidae) are described. Roa semilunaris sp. nov., based on six specimens from the Mascarene Ridge (south-western Indian Ocean), is most similar to Roa jayakari (Norman, 1939), distributed in the Red Sea and the northern Indian Ocean, in having scales on the upper jaw, interrupted pale lines within the second dark body band, and similar coloration and shape of the pelvic fin. However, the former is readily distinguished from R. jayakari by a wider whitish interspace between the second and third black bands [width of interspace at lateral line level 15.9%-18.5% of standard length (SL) in R. semilunaris sp. nov. (vs. 5.1%-8.5% of SL in R. jayakari)], with 9 or 10 pored lateral-line scales in the interspace (vs. 3-5); an oval or semicircular ocellated blotch on the soft-rayed portion of the dorsal fin (vs. a circular blotch); the head higher and longer [head length 35.0%-36.7% of SL (vs. 40.8%-44.1% of SL), head height 48.1%-50.5% of SL (vs. 52.0%-56.9% of SL)], and postorbital length 14.0%-15.1% of SL (vs. 17.0%-20.5% of SL). Roa uejoi sp. nov., based on three specimens from Guam (Mariana Islands), is most similar to Roa excelsa (Jordan, 1921) (now restricted to the Hawaiian Islands and Johnston Island), but is distinguished from the latter by having a circular dorsal-fin ocellated spot (vs. spot distinctly oval in the latter) and a much more elongate, filamentous first pelvic-fin soft ray, of length 119.0%-123.4% of 2nd ray (vs. not obviously filamentous, 104.9%-105.8%). A key to the eight valid species of Roa is provided.