Abstract
Hard coral species in the agariciid genus Pavona are common in shallow and mesophotic coral reef communities across the Indo-Pacific, but their taxonomy has long been overlooked. Pavona giannii sp. nov. is here described based on newly collected material across the Indian Ocean, and historical museum specimens. In vivo and skeletal morphological features are described, diagnostic characters measured, and comparison with congeners performed. The new species forms an encrusting corallum devoid of raised ridges on its surface. Its corallites are flush with the surface, not inclined, and less than half a corallite diameter apart. Corallites arrangement is thamnasteroid and series can form locally. Where they occur, the radial elements run over the shared walls to the adjacent series' corallites creating a ladder-like arrangement similar to that observed over the ridges in congeners like Pavona varians and Pavona chiriquiensis. Despite the lack of ridges, P. giannii sp. nov. has morphological affinities with these two species. However, based on previously published morphometrics and meristics, P. giannii sp. nov. corallites are larger and more crowded, and the primary septa are longer and more numerous. In vivo, the new species is distinguished by fully extended white to beige tentacles during the daytime, giving it a white-bearded appearance. Despite the ecological relevance of Pavona corals, a taxonomic revision of the genus is overdue, and the existing molecular studies indicate that it is polyphyletic. Here, the proposed placement of P. giannii sp. nov. in the genus is based on morphological evidence alone and phylogenomic analyses are currently in progress.