Description
Dorsal spines (total): 14; Dorsal soft rays (total): 14-16 (usually: 15); Anal spines: 2; Anal soft rays: 13-14 (usually: 13); Pectoral fin rays: 19; Lateral line scales: 19 tubes. More than 20 predorsal scales. Head scaly above to before nostrils, naked only on anterior parts of snout, preorbital and chin, where there are pores, and on mouth. Maxillary not reaching below eye. Teeth compressed, uniserial. Mandibular ramus very slightly raised. Suborbital serrate, not notched. Posterior preopercular limb serrate. Other opercles entire. Cheek-scales in three or four rows. A small, exposed opercular spine. Suborbital scales extend forward to below anterior part of eye. Interorbital roundly convex. Thirteen slender, spinose gill-rakers on lower part of first branchial arch. Body deep, robust anteriorly, compressed posteriorly, covered with ctenoid scales with five or six basal radii and scored or pitted surfaces. Some auxiliary scales on head and shoulder-region. Scales, some lanceolate, extend thickly over bases of the fins, except ventrals, which have axillary scales. Base of spinous dorsal much longer, than that of soft; Membrane not incised or pennanted. Fin-lobes rather rounded, except paired fins which are more pointed. Ventrals reaching vent. Max. length: 15.0 cm TL. Depth range: 1 - 30 m.

Color
Body and head color primarily brown, yellow-orange on ventral portion. A blue streak runs from the snout to the suborbital. Blue or purplish spots are on opercular series. Each scale with dark brown streak near its margin, appearing as series of narrow transverse bands. The dorsal is fin brown, posteriormost is somewhat translucent. The caudal fin is tan to brown, outermost part translucent to yellowish. The anal and pelvic fins yellow to orange. The pectorals are transparent with suffusion of yellow with a small dark spot superiorly at its base.

Etymology
Plectroglyphidodon: from Greek, plektron = anything to strike with, spur + from Greek, glyphis = carved + from Greek, odous = teeth.
gascoynei: named after H.M.A.S. Gascoyne, from aboard which the new species was collected during a survey of the islands in the Coral Sea. Two ships of the Royal Australian Navy have been named HMAS Gascoyne, after the Gascoyne River, the longest river in Western Australia. HMAS Gascoyne (K354/F354/A276) was a River-class frigate that served in the Royal Australian Navy (RAN). Laid down in 1942 and commissioned in 1943, the frigate served during World War II, before being placed in reserve in 1946. Reactivated in 1959, Gascoyne was reclassified as a survey and research ship, a role she fulfilled until she was decommissioned again in 1966, and sold for scrap in 1972.
Original description: Pseudopomacentrus gascoynei Whitley, 1964 - Type locality: Kenn Reef, Coral Sea.

Distribution
Southwestern Pacific: Coral Sea east to New Caledonia and Kermadec Islands, south to northern New Zealand.

Biology
Adults inhabit coral and rocky reefs. Oviparous, distinct pairing during breeding. Eggs are demersal and adhere to the substrate. Males guard and aerate the eggs.