Scientists have discovered a fish that looks like a seahorse but is not one

The new species has been named Australyichthys aegis. It is no longer than a human thumb.

In appearance, the fish is almost indistinguishable from a seahorse: it has the same curved head, a prehensile, coiled tail and, in males, a fully enclosed brood pouch in which the offspring develop.

This is precisely why it was classified within the seahorse genus for many years.

Details

The only known specimen of the new species was accidentally retrieved from the seabed off the southern coast of Australia back in 2006 during an expedition studying marine invertebrates.

As the scientists were not looking for fish at the time, but for brachiopods, the specimen was mistakenly sent to the invertebrate collection at the South Australian Museum, where it lay unnoticed for many years.

To date, only seven specimens of this genus are known, all collected by chance over the past 65 years.

As the scientists were unable to dissect the rare museum specimens, they used micro-computed tomography, which enabled them to create three-dimensional models of the skeletons.

It turned out that the internal structure of these fish differs significantly from that of true seahorses. For example, they lack the characteristic bony ‘crown’ on the head and the distinctive structure of the abdominal region.

Further DNA analysis confirmed the findings: Australyichthys does not belong to the seahorse genus, although it is a close relative.

According to the researchers, the discovery is a striking example of convergent evolution — a situation in which unrelated organisms independently develop an almost identical appearance due to similar lifestyles.

It appears that the characteristic body shape of the seahorse has evolved within the family of pipefish at least twice.

No one has ever seen these fish alive

All known specimens were accidentally caught in trawl nets at depths of between 50 and 125 metres. No one has yet observed these fish in their natural habitat.

The authors consider them to be so-called ‘lost species’ — organisms known only from a few museum specimens. This does not mean that they have disappeared, but it does highlight the need for specialised search expeditions.

Source

Study: Graham Short et al.

Australyichthys gen. nov. (Teleostei, Syngnathidae), a lost mesophotic lineage from southern Australia…

Journal: Journal of Lost Species (2026).