FlatheadsPlatycephalidae

There are two ways for a fish to end up flat, and this is the cheap one. A flounder lies on its side and has to rebuild its skull to do it. A flathead never turned over: it is an ordinary fish pressed down from above, the skull spread wide and flattened, the eyes carried up onto the roof of the head, the jaws still hinged the way any fish's jaws are hinged. Nothing had to be rearranged internally, which is why a flathead still looks like a fish and a flounder does not.

The head is the equipment. It is a bony wedge, ridged and spined like a piece of machinery, with spines on the gill covers that anyone who handles one finds out about, and it does two jobs at once. It holds the eyes up where they command the whole water column overhead, and it holds a mouth that opens upward. Anything crossing above is taken from below in a movement most people only register afterwards as a puff of settling sand.

The large ones are female. In the species that have been studied a flathead spends the first part of its adult life as a male and changes to female as it grows, so size and sex are the same variable: a meter of fish on the sand is a female with years behind her, and the smaller fish around her are males. That makes the standard fishery habit of keeping the biggest fish a way of removing the breeding females first, and flatheads are a serious commercial catch from the Gulf across to 🇦🇺 Australia.

Three species are listed here and they cover the family's range: one the size of a matchbox, one reaching a meter, and the crocodilefish that everybody photographs. None of them are coral animals. They belong to the open bottom beside the reef, on sand, rubble and seagrass, from the shallows down past the depth most dives end, and they hunt by staying exactly where they are until something passes over.