G. Morphological-comparison-of and . Obesus, with congeneric species Measurements on Gymnocranius obesus sp. nov. specimens are provided in Table 1 and in Supplementary Table S1. Homologous measurements on reference specimens of G. griseus and Gymnocranius sp. D are provided in Supplementary Tables S2 and S3, respectively. Morphological features including body shape, caudal fin shape, and pigmentation patterns are here compared across 12 Gymnocranius species, including all 10 species currently recognized as valid

G. Frenatus, G. Grandoculis, G. Microdon, G. Oblongus, G. Satoi et al., The remaining five species Gymnocranius sp. D and G. obesus sp. nov. do not possess blue ornamentation on snout and cheek. Gymnocranius audleyi has a distinctive parietal scale patch and G. elongatus has a distinctive swallow-like tail. The confusion of G. obesus sp. nov. with juvenile or pre-adult G. grandoculis [28], was possibly due to the fact that the patterns of dark bars on the flank are similar between the two species, with the fourth dark bar running from the base of the sixth or seventh spine of dorsal fin to the origin of anal fin (Table 3). However, the body is more slender in G. grandoculis and the colour of the anal fin in adult G. grandoculis is different (Table 3) Additional characters are needed for the morphological distinction of G. obesus sp. nov. from the remaining two species, namely G. griseus and Gymnocranius sp. D. The lectotype of Dentex (= Gymnocranius) griseus (Supplementary Fig. S2A) had a ratio of SL to BD of 2.6; the eye diameter (ED) was 7.9% of SL. As pointed out previously by specialists of the family Lethrinidae [1, 26], the exaggeratedly elongate shape of the lectotype may reflect distortion caused by the preparation of the dried specimen. Measurements on the drawing representing G. griseus in C.J. Temminck and H. Schlegel's original description (plate 36 of [10]) were the following: ratio of SL to BD = 2.25; ratio of SL to HL = 3.4; ratio of ED to length of caudal fin's median ray (MRC) = 0.89. Neither the body shape of the presumably distorted lectotype of G. griseus nor that of the lithography accompanying the description can be considered as representative of the species. A particular morphological feature enabled us to distinguish G. obesus sp. nov. from G. griseus: the number of front scales on the top of head, Several species in the genus Gymnocranius, including We counted four to six front scales (Fig. 2) in G. obesus sp. nov., while nine to eleven were present in G. griseus, including the lectotype, which had nine (RM, pers. obs.; Supplementary Fig. S4). Last, G. obesus sp. nov. differed from G. griseus by the dark-bar patterns on flanks. While the fourth transversal dark bar in G. obesus sp. nov. ran from the basis of the sixth spine of the dorsal fin down to the origin of the anal fin, that in G. griseus, when visible, ran down from the base of the sixth dorsal spine to the abdomen

. Gymnocranius-obesus-sp and . Nov, Eye diameter (ED) was about equal to or larger than the IOW (ratio of ED to IOW = 1.0-1.3) and generally found to be larger than the MRC, with a ratio of ED to MRC = 1.0-1.2 (Table 1, Supplementary Table S1) while the eye diameter of both Gymnocranius sp. D and G. griseus was generally smaller than both the IOW and MRC (Supplementary Tables S2 and S3) Other body proportions did not clearly differ between G. obesus sp, nov., G. griseus, and Gymnocranius sp. D (Table 1; Supplementary Tables S1-S3): the ratio of SL to BD was 2.2-2.4 in G. obesus sp. nov., vs

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