The black-and-orange juvenile behaves nothing like the plain adult it becomes.
Adults reach about 45 cm and are unremarkable silver-grey disc-shaped fish of outer reefs and drop-offs. The juvenile is the reason the species appears on a muck diver’s list: jet black, with every fin edged in a broad band of brilliant orange, and with the dorsal and anal fins extended into long lobes that make the body appear far larger than it is. Juvenile Platax orbicularis and P. teira occupy similar habitat and are separated on the fin margin — orange and continuous in pinnatus, absent or brown in the other two.
Juveniles are found singly in shallow water, under ledges and overhangs, beside jetty pilings and against dark backgrounds where the black body reads as shadow. They swim with a slow rocking undulation on their side, a motion widely described as mimicry of a toxic flatworm or a polyclad; this is a plausible and often-repeated interpretation rather than a tested one, and the fish’s habit of staying in deep shade is at least as good an explanation for the shape. The juvenile stage is brief, so a fish found one week may be gone or half-changed the next. Recorded from about 3 to 25 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.