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[[ Genus Lethrinus Valenciennes ]]
Species of the genus Lethrinus , the emperor fishes, remain among the most problematic tropical marine coastal fishes to identify (Smith, 1959; Walker, 1975; Sato, 1978; Carpenter& Allen, 1989; Carpenter, 2002). Most of the 29 known species of Lethrinus are large and economically important. However, their meristic and morphometric characteristics are conservative making many difficult to differentiate taxonomically. The Lethrinidae is a sister taxon to the Sparidae plus Centracanthidae and together with the Nemipteridae comprise the Sparoidea (Carpenter and Johnson, 2002). The systematic relationships among the five genera of Lethrinidae are as yet unknown, but species of Lethrinus are easily distinguished from the other four lethrinid genera ( Gnathodentex Bleeker, 1873 ZBK ; Gymnocranius Klunzinger, 1870 ZBK ; Monotaxis Bennett, 1830 ZBK ; Wattsia Chan & Chilvers, 1974 ZBK ). A phylogeny of most species of emperors has been inferred using molecular systematics (LoGalbo, et al., 2002). Three groups of emperors can be delineated based on dentition and body shape (Carpenter, 1996). These are: high bodied species with molariform teeth, high-bodied species with conical teeth, and low-bodied species with conical teeth. Most of the 12 species that comprise the third group, including the new species described here, appear to form a distinct clade of closely related Indo-Pacific species that prey upon other fishes and mobile invertebrates (LoGalbo et al., 2002).
The purpose of this paper is to newly describe Lethrinus ravus ZBK , and compare it to its proposed sister taxon, L. semicinctus Valenciennes in Cuvier and Valenciennes ZBK (1830). Sato (1978) considered the species L. semicinctus ZBK to include two forms. These forms are nearly identical in all meristic and other morphological characteristics except that one has a prominent oblong dark blotch on the sides straddling the lateral line below the soft dorsal fin (Fig. 1a). Carpenter (1989, 2001) considered the two forms as distinct species based on consistent co-occurring differences in color pattern in the Philippines. In addition, he found consistent differences in average number of total scales found in the supratemporal patch of scales. LoGalbo et al. (2002) confirmed these two species are distinct sister species using complete sequences of the cytochrome b gene. Based on type descriptions and examination of type material, the body form with the dark lateral blotch clearly represents L. semicinctus Valenciennes (in Cuvier and Valenciennes, 1830) ZBK while the other form is undescribed (Carpenter & Allen, 1989).