A common sole resting on a harbour mudflat is one of the harder things to see in a New Zealand estuary. Greenish-grey above with faint mottling, body pressed flat against the sediment, it is very close to invisible until it moves. When startled it produces a brief burst of speed, relocates a metre or two away, and becomes invisible again almost immediately. This is the entire defensive strategy, and it works well enough that the species has made a successful living in shallow coastal habitats throughout New Zealand for a very long time. Peltorhamphus novaezeelandiae is a flatfish, a righteye flounder in the family Rhombosoleidae, endemic to New Zealand. Like all flatfish it begins life as a bilaterally symmetrical larva with one eye on each side of the head. During metamorphosis the left eye migrates across the top of the skull to join the right, and the fish settles permanently onto its left side. The upper surface, now carrying both eyes, develops cryptic pigmentation. The underside remains white. In the common sole this produces a fish that is oval, thin, and smooth-edged, from 25 to 45 centimetres long, with a long filamentous ray on the upper pectoral fin that distinguishes it from the other New Zealand sole species. The rostral hook, which in this species covers the mouth on the eyed side, is another useful identifying feature. The species is nocturnal. During daylight it rests on the bottom, often partially buried in sediment by rippling the marginal fins and shuffling gently downward until only the eyes and the top of the head remain visible. After dark it forages across soft substrate for amphipods, crabs, shrimps, and worms, moving slowly and detecting prey by contact and smell rather than vision. Juveniles spend up to two years in estuarine nursery habitats, shallow mudflats and sandflats in sheltered harbours, before moving to deeper inshore waters as adults. This nursery dependence makes estuary condition a relevant factor in population health. The species is more abundant in the South Island than the North, consistent with its preference for cooler, more productive soft-sediment environments. Common soles are taken commercially under the Quota Management System and are regarded as good eating. They are also caught recreationally by net and line in estuaries and sheltered bays. The population is considered stable, and the species carries no conservation concern. It simply gets on with being flat and invisible, which turns out to be a very effective long-term plan.