Coradion calendula, a new butterflyfish from Australia (Teleostei: Chaetodontidae).

The new butterflyfish, Coradion calendula, is described on the basis of 44 specimens collected off Western Australia, the Northern Territory, and north Queensland, Australia. The new species is most similar to Coradion chrysozonus, with which it shares IX dorsal-fin spines, a single ocellated spot on the soft-rayed portion of the dorsal-fin, and a single dark band on the frontal surface of the thorax. The new species is distinguished from C. chrysozonus by slightly higher ranges of dorsal-fin soft rays 28–32, mode 29 (vs. 27–30, mode 28) and anal-fin soft rays 20–22, mode 21 (vs. 18–21, mode 20); an orange band on the caudal peduncle in fresh specimens (lost after preservation) with a saddle-like blackish dorsal streak (vs. a broad brown -to-black circumpeduncular band in both fresh and preserved specimens); a sharply pointed pelvic fin with an almost straight posterior contour when spread (vs. a rounded pelvic fin with an expanded posterior contour); and a dark band on each interopercle joining on the ventral midline, with their anterior margins forming a sharply pointed “V” in ventral view (vs. separated by a relatively wide interspace). Despite well-defined morphological and coloration differences, the mtDNA difference between the two species was relatively low, 0.8–1.9% (mean 1.3%) and 2.9–7.5% (mean 4.8%) pairwise sequence difference in COI and control region genes, respectively. Morphological and color-pattern characters and mtDNA lineage were not concordant in some specimens from northern Australia, where the two species overlap, suggesting that the two species hybridize at their common biogeographic borders.