A ghost shark hiding at 800 meters off Costa Rica turned out to be brand new to science

In the cold, lightless water nearly half a mile beneath the Pacific off Costa Rica, a strange fish with a blade-like snout and dead-black eyes had been slipping into fishing gear for decades without anyone realizing what it was. In 2026, a team of scientists finally settled the question, announcing that the animal was not a known species at all but one entirely new to science. The discovery adds a fresh branch to one of the most ancient and least understood lineages of fish alive today.

A new name for a long-nosed ghost

Researchers formally described the fish as Rhinochimaera costaricana, naming it for the country in whose waters it was found. According to Newsweek’s account of the discovery, the description was based on three male specimens collected off the coast of Puntarenas at depths ranging from roughly 390 to nearly 790 meters, and the work was published in the scientific journal Zootaxa in mid-2026. The species belongs to a small, cryptic group of cartilaginous fishes known as long-nosed chimaeras, whose distinguishing feature is exactly what the genus name suggests: an elongated, paddle- or blade-shaped snout studded with sensory organs that helps the fish detect prey in total darkness.

Why “ghost shark” is a misleading nickname

The popular label ghost shark conjures images of a shark, but chimaeras are only distant cousins of sharks and rays. All three belong to the cartilaginous fishes, whose skeletons are made of cartilage rather than bone, but the chimaera lineage split away from sharks hundreds of millions of years ago and has followed its own evolutionary path ever since. The result is a creature that looks assembled from spare parts: large, iridescent eyes adapted to near-total darkness, smooth scaleless skin, tooth plates instead of the replaceable rows of teeth sharks are known for, and a venomous spine in front of the dorsal fin. Males also carry a peculiar retractable appendage on the head thought to play a role in mating, one of the many features that make the group biologically distinctive.

Hidden in plain sight for years

What makes the find remarkable is that the animal was not truly undiscovered so much as unrecognized. Specimens had been turning up sporadically for years, often as bycatch hauled up by deep-water fishing operations, but they had been lumped in with similar-looking relatives. Reporting from the Tico Times on the announcement noted that the species was pinned down only after researchers combined careful anatomical comparison with modern genetic tools that could separate it from its close kin. The study was a collaboration among Costa Rican institutions, including the University of Costa Rica and the country’s fisheries and aquaculture institute, working alongside a Brazilian university, with a Costa Rican biology student credited as the paper’s lead author.

Life in the deep-sea twilight

The world the fish inhabits helps explain why it stayed hidden. At the depths where it lives, sunlight has all but vanished, the water is frigid, and pressure is crushing, an environment that is expensive and technically demanding for scientists to reach. Long-nosed chimaeras like this one cruise slowly along or just above the seafloor, using the electroreceptors and other sensors packed into that long snout to find the worms, mollusks, and small invertebrates they crush with their tooth plates. The genus Rhinochimaera is known from deep waters in several of the world’s oceans, but its members are encountered so rarely that even basic details of their behavior, reproduction, and range remain poorly documented.

What one new fish says about the ocean’s blank spots

A single new chimaera might seem like a footnote, but discoveries like it underscore how little of the deep ocean has been catalogued. The deep sea is the largest habitat on the planet, and the overwhelming majority of it has never been surveyed in detail, meaning that even relatively large animals can go unnamed for decades. Each new description sharpens the picture of biodiversity in these zones and provides a baseline against which scientists can measure change, an increasingly urgent task as deep-sea fishing and interest in seabed mining push human activity into waters that were once effectively out of reach.

The role of genetics in modern discovery

The Costa Rican ghost shark also illustrates how the work of naming species has changed. Where earlier naturalists relied almost entirely on outward appearance, today’s taxonomists pair anatomy with DNA analysis, which can reveal that animals long assumed to be the same are in fact separate species that simply look alike. That toolkit is steadily uncovering hidden diversity across the tree of life, and nowhere is the payoff larger than in the deep sea, where physical access is hardest and the odds of overlooked species are highest. In this case, the genetic evidence was what finally distinguished the newcomer from its relatives and justified giving it a name of its own.

For now, Rhinochimaera costaricana joins the sparse roster of known long-nosed chimaeras, a fish that spent years passing through fishing nets before anyone recognized it as unique. Its formal debut is a small reminder that the deep water off familiar coastlines still holds creatures no one has ever properly seen, waiting in the dark for the right combination of a net, a specimen, and a scientist with the tools to tell them apart.

This article was produced with the assistance of AI and reviewed by the Morning Overview editorial team.

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