Australyichthys

Australyichthys is a genus of seahorse-like ray-finned fishes in the family Syngnathidae, endemic to the temperate mesophotic ecosystems of southern Australia. It was named in 2026 by Short, Foster, Gomon and co-authors, and comprises three species: the type species A. minotaur, A. paradoxus, and A. aegis. All known specimens derive from structurally complex benthic habitats at depths of approximately 50–124 metres (164–407 ft).

Members of the genus resemble true seahorses (genus Hippocampus) in external morphology, including their possession of a ventrally angled head (angled toward the animal's underside), a fully enclosed male brood pouch, and a prehensile tail; initially, A. minotaur and A. paradoxus were indeed assigned to the seahorse genus Hippocampus due to these characteristics. Genetics-based phylogenetic analyses would, however, place Australyichthys within Haliichthyini, a tribe in the pipefish subfamily Syngnathinae distant from Hippocampus (tribe Hippocampini). Its hippocampiform body plan is therefore the result of convergent evolution. The genus is represented by only eight specimens collected incidentally over nearly eighty years, none within the last two decades, and has not been observed alive. On this basis, it has been regarded as a "lost" taxon.