Lives in drifting weed rather than on the bottom, and arrives with whatever the current brings.
The only frogfish that lives in open water, reaching about 20 cm and found worldwide in warm seas wherever floating Sargassum collects. The body is mottled cream, olive and brown, broken by pale streaks and fringed with weedy skin flaps that repeat the outline of the alga around it. The pectoral fins are jointed and hand-like as in other frogfish and are used to grip weed rather than to walk on sand. Within its habitat there is nothing to confuse it with; the difficulty is seeing it at all against the material it lives in.
Cannibalism is routine, and the species will take prey close to its own length. Eggs are laid in a floating gelatinous raft. Because it is carried rather than resident, its appearance at any muck site is a matter of what the current has delivered: it turns up in weed rafts and around floating debris in the top few metres, usually inshore after a period of onshore wind, and is gone again with the next tide. That makes it one of the least predictable animals on this list and one that is worth asking the boat crew about, since a raft spotted from the surface is easier to find than the fish inside it.
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.