Descriptions of four new species of damselfishes (Pomacentridae) in the Pomacentrus philippinus complex from the tropical western Pacific Ocean.

Four new species of Pomacentrus, allied to P. philippinus, are described from the western Pacific Ocean. Pomacentrus albiaxillaris, n. sp. is described on the basis of 81 specimens, 14.5–70.0 mm SL, from the Palau Archipelago in Micronesia. It was formerly considered to be a Palauan population of P. emarginatus Cuvier, a species of uncertain status from Waigeo in West Papua. However, the two species differ in appearance and morphology and the new species from Palau has never been observed at Waigeo and surrounding areas despite extensive surveys by the authors. Pomacentrus albiaxillaris differs from other members of the philippinus complex in possessing a white pectoral-fin axil; a small dark spot that is restricted to the uppermost portion of the pectoral-fin base (instead of a large black marking that covers the entire fin base); a whitish caudal fin; and a bright blue dorsal scleral surface of the eye. Pomacentrus flavoaxillaris, n sp. is described on the basis of 28 specimens, 49.5–72.9 mm SL, from Micronesian locations east of Palau, including Ulithi Atoll, Chuuk, Pohnpei, and Kosrae. Additional photographic and literature records include Ngulu Atoll, Yap, and the Mortlock Islands. It is similar to P. albiaxillaris n. sp. in having a white caudal fin and blue dorsal scleral surface of the eye, but differs in having a yellow inner pectoral-fin axil, a large black spot covering the entire pectoral-fin base, white zones at the bases of the posteriormost dorsal- and anal-fin rays, and a whitish caudal peduncle. Pomacentrus magniseptus, n. sp. is described from 24 specimens, 34.6–75.6 mm SL, collected at the Great Barrier Reef of Australia. It differs from other members of the philippinus complex by its unique color pattern, consisting of horizontal rows of pale spots on the side of the body and entirely blackish median fins. It also differs from most relatives in always lacking scales on the preorbital and most of the suborbital. Pomacentrus nigriradiatus, n. sp. is described on the basis of 48 specimens, 28.8–86.9 mm SL, from Samoa, Rotuma, Wallis Island, Loyalty Islands, New Caledonia, and Vanuatu. Diagnostic features include highly contrasting dark fin rays on the posterior portions of the dorsal, anal, and caudal fins, as well as the lack of a contrasting marking on the inner pectoral-fin axil. It also differs from P. albiaxillaris and P. flavoaxillaris in usually having at least a few scales on the preorbital. Genetic evidence is also provided to resolve relationships among the four new species and P. philippinus. The divergence in the mtDNA sequence of three concatenated markers between these species ranges from 5.1–7.4% (in average pairwise distances), with the closest relationship between P. flavoaxillaris and P. magniseptus. The four new species differ by an average of 12.9% in mtDNA sequence from the type population of P. philippinus in the Philippines