A soft-coral feeder whose yellow-and-blue juvenile looks nothing like the plain black adult.
Adults reach about 18 cm and are uniformly blue-black to black, with a dark spot at the base of the pectoral fin and sometimes a slightly paler belly. Juveniles are a different-looking fish entirely: yellow over the flanks and belly, blue-black over the back, with a black stripe through the eye and a black margin to the dorsal fin. Divers who have seen only one of the two stages routinely record them as separate species, and the change is gradual enough that half-converted subadults, dark above and still yellow below, are common.
Its congener the bluestreak damselfish Neoglyphidodon nigroris passes through an equally drab adult stage. The separation is that adult melas is uniformly dark to the tail while adult nigroris keeps a yellowish or pale tail and a dark bar at the tail base. As juveniles they are easy: melas is yellow with a single eye stripe, nigroris is yellow with two long black stripes running the length of the body. Cross’s damselfish Neoglyphidodon crossi, which is restricted to Indonesian waters, has an orange-red juvenile with blue lines and is a third member of the same problem.
It feeds largely on soft coral polyps, taking Sinularia, Sarcophyton and Xenia, which is unusual among damselfishes and ties it to soft coral colonies rather than to branching hard coral. Because soft corals persist on silty rubble slopes, it stays ordinary at the muck destinations. Adults are territorial and will hold position against a diver at close range; juveniles are strongly site-attached to a single colony and can be relocated on later dives. Recorded from the shallows to about 15 m.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.