Researchers have given a scientific name to a new species of deep-sea ghost shark hauled from Pacific waters off Costa Rica at depths reaching roughly half a mile below the surface. The animal, formally described as Rhinochimaera costaricana, is built from three male specimens that fishery scientists collected between 2000 and 2023 at depths of 390 to 787 meters, far below where recreational divers can reach. Naidely Valeria Vidaurre Quesada, a biology student at the University of Costa Rica who led the description, published the findings with colleagues from the country’s Fisheries and Aquaculture Institute and Brazil’s Federal University of Pará.
The designation rests on genetics as much as anatomy. DNA sequences from the three specimens diverged 3.9 percent to 4.7 percent from every other known Rhinochimaera species, a gap well above the threshold taxonomists typically use to separate one species from another. That distance, combined with body measurements that did not match any previously catalogued animal, persuaded the team that the Costa Rican specimens belonged to a species no one had described before.
Three specimens collected over 23 years
None of the three specimens came from a single expedition. Fishery researchers pulled them from the Pacific coast of Costa Rica at different times between 2000 and 2023, each one landing in a scientific collection years before anyone matched them to a distinct species. All three were male, collected at depths between 390 and 787 meters — roughly a quarter-mile to half a mile down — a range so far below the surface that the fish are never encountered by swimmers, snorkelers or the recreational submersibles now common in shallower reef tourism. Depths in that range sit within what oceanographers classify as the bathyal zone, a stretch of ocean defined by near-total darkness and near-freezing water that begins a few hundred meters below the surface and extends to roughly 4,000 meters.
That collection gap is typical of deep-sea taxonomy. Specimens can sit in institutional storage for decades before a researcher with the right comparative dataset recognizes what has actually been sitting on the shelf, and Vidaurre Quesada’s description is a case study in exactly that lag.
Vidaurre Quesada’s genetic case for a new species
To confirm the specimens represented something new, Vidaurre Quesada’s team compared 49 body measurements from the three fish against data from more than 90 individuals representing the three previously recognized Rhinochimaera species. The comparison turned up consistent differences in proportions, but it was the DNA divergence, 3.9 percent to 4.7 percent from the closest relatives, that made the strongest case, since morphology alone can blur between closely related deep-sea fish that rarely surface for study.
The findings appeared in the taxonomic journal Zootaxa, the standard venue for formally naming new animal species, placing Rhinochimaera costaricana on the scientific record for the first time since the genus itself was described more than a century ago.
A fourth chimaera in a genus short on names
Rhinochimaera costaricana becomes the fourth recognized species in its genus worldwide and the first described from the Eastern Pacific, filling a geographic gap in a group whose other members are known from the Atlantic and the Indo-Pacific. Chimaeras, the broader family that includes ghost sharks and ratfish, are cartilaginous fish related to sharks and rays but separated from them on the evolutionary tree for hundreds of millions of years, distinguished by long snouts, large eyes adapted to darkness and a single pair of gill slits.
Popular coverage has nicknamed the new species a ghost shark, a label that has stuck to chimaeras generally because of their pale coloring and their habit of drifting, largely unseen, through waters no diver visits. The genus’s other members include Rhinochimaera pacifica, found more broadly across the Pacific, along with relatives documented in the Atlantic and the Indo-Pacific; none had previously been confirmed off Central America’s Pacific coast, which is what made the Costa Rican specimens worth a formal genetic comparison rather than an assumption that they belonged to an already-known species.
Like other chimaeras, the new species likely relies on a single venomous spine in front of its dorsal fin for defense rather than the rows of replaceable teeth associated with true sharks, and its elongated, flattened snout is built to probe soft sediment for the worms, mollusks and crustaceans that make up a typical chimaera diet.
The deep Pacific keeps yielding new chimaeras
Costa Rica’s Pacific slope drops quickly into water deep enough that most of it has never been directly surveyed, and fishery bycatch, animals caught incidentally during commercial trawling rather than targeted research dives, remains one of the few ways specimens from that depth reach scientific collections at all. INCOPESCA’s role in supplying the specimens reflects that reality: much of what is known about deep-sea Costa Rican fish comes from institutions monitoring commercial catches rather than from dedicated deep-sea expeditions.
A species confirmed only from bycatch specimens complicates any future conservation assessment, since population counts, breeding grounds and vulnerability to fishing pressure cannot be estimated from three male fish collected more than two decades apart. Formal description is nonetheless the necessary first step: an unnamed animal cannot be tracked, protected or studied systematically, no matter how many individuals eventually turn up in a net.
Vidaurre Quesada’s team has not said whether additional specimens are expected, and with only three fish anchoring the description, basic questions about the species, its range, its diet, how common it actually is along the Costa Rican coast, remain unanswered for now.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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