Micro-CT scans and DNA show three deep-water fish from southern Australia, long filed as seahorses, belong to a separate lineage that evolved the same body shape independently.
Three small deep-water fish from southern Australia that were long classified as seahorses have been placed in a genus of their own, according to a new study described by its authors, Graham Short and David Harasti, in a piece distributed by The Conversation and ScienceDaily. The fish share the seahorse look: a down-tilted horse-shaped head, a curled gripping tail and, in males, an enclosed brood pouch. The authors named the genus Australyichthys and nicknamed its members "sea muppets": the helmethead sea muppet (Australyichthys aegis), the bullneck sea muppet (A. minotaur) and the paradoxical sea muppet (A. paradoxus). The study is reported as published in the Journal of Lost Species.
The whole genus is known from only seven specimens collected over about 65 years across more than 2,500 kilometres of coastline, all brought up by accident in trawl nets or dredges working the seafloor at roughly 50 to 125 metres, and nothing has been collected in nearly two decades. The single specimen of A. aegis was dredged in 2006 near the Gambier Islands, at the mouth of South Australia's Spencer Gulf, during an expedition targeting shelled invertebrates, and was misfiled in the South Australian Museum's invertebrate collection. Because the specimens are irreplaceable, the researchers did not dissect them; they used micro-CT scanning to build three-dimensional skeletal models and compared them bone by bone with true seahorses (Hippocampus).
The scans showed the fish lack the rigid cage of fused bony plates supporting the belly and the bony crown, or coronet, found on seahorses, and instead have a different arrangement of belly-supporting bones. DNA sequenced from the A. aegis specimen, which had been preserved in ethanol rather than formalin, placed the fish outside the seahorses, on the branch closest to them. The authors say this shows the seahorse body plan arose at least twice within the family Syngnathidae, which also includes pipefishes, pipehorses and seadragons, a case of convergent evolution. They stress that "lost species" is not a prediction of extinction: no one has ever seen these fish alive, and they argue the animals are most likely still on the Great Southern Reef's little-explored deeper zones, making them a priority for targeted surveys. The findings come from a single source and have not been independently reported here.
