Facebook Twitter Pinterest Well hidden: Porophryne erythrodatylus. Photograph by K Sebo, reproduced by permission of American Society of Ichthyologists and Herpetologists

If you are having difficulty seeing a fish in the photograph, well, that is rather the point. This newly discovered genus and species of frogfish mimics the appearance of the algae-encrusted, small sponges among which it may be found in subtidal, rocky reef habitats. Two extremely distinct colour phases are found within this single new species. First is a grey phase that is about the same colour as the Psammocinia sponges it hangs out with. It has naked black spots in an asymmetrically scattered pattern on the head and body and few or no cutaneous appendages on its body. Second is a decidedly more colourful and variable phase that comes in red, pink, orange, yellow and/or white that is found in association with sponges of the genus Darwinella that, you guessed it, are yellow or red in colour.

Rachel Arnold and Theodore W Pietsch of the University of Washington, Seattle, with colleague Rob Harcourt of Macquarie University, Sydney, have named the new genus and species of frogfish Porophryne erythrodactylus. A member of the family Antennariidae, a specimen was first collected in 1980 but was subsequently lost, and no others were procured until 2005, and again in 2009, when scuba divers gathered specimens near Kurnell and Bare Islands in Botany Bay, New South Wales, Australia. It could be argued that they are easier to lose than many fish as they are only 60-75mm long. Porophryne most closely resembles Kuiterichthys, but is distinct in several ways including red pigmentation along the distal margins of its fins, fewer anal fin rays details of the structure of the first and second dorsal fin spines, and in the esca.

Adult female antennariids, like most anglerfish, have an esca – a swollen organ at the tip of a highly modified dorsal ray in which reside symbiotic luminescent bacteria and which is dangled over the head like a fishing pole. Interestingly, in some anglerfish the bacteria in the esca cannot create light on their own, requiring certain chemicals provided by the host fish in order to luminesce. The stunning images of the anglerfish found in the total darkness of the deep sea are of those in the family Ceratiidae. The new species and others in its family are found instead on the continental shelf, as are fish of the related monkfish family Lophiidae. Such benthic forms are dorso-ventrally compressed in body shape, whereas pelagic or open-water forms are laterally compressed. The fish-bacterium symbiosis is an ancient one, with mitochondrial genome data suggesting an origin of anglerfish between 100m and 130m years ago.

As with most new species, scientists are still discovering the geographic range of P erythrodactylus. So far, specimens are known from six to 24 metres’ depth in the near-shore waters of Botany Bay, with credible sightings as far south as Jervis Bay. Some frogfish have been observed to hop along the seafloor when disturbed. Others use a sustained form of “jet propulsion” to put distance between themselves and threats. P erythrodactylus has been observed to do neither. Instead, it darts quickly but only for a short distance. When repeatedly bothered by divers, one individual kept its tail tightly curled and dorsal fins splayed while making no effort to swim away even when picked up and dropped to the seafloor several times. As there is no evidence of toxicity in the group, simply trying to look large while playing dead seems to be the back-up defence when camouflage fails.