Wednesday, 22 February 2017

Hydrolagus erithacus: New Species of Ghost Shark Discovered

Photo of the Hydrolagus erithacus ghost shark
Kristin Walovich holds the newly described species of ghost shark
Photo Credit: Kristin Walovich

Researchers recently announced the discovery of a new species of ghost shark, Hydrolagus erithacus. Ghost sharks - which aren’t actually sharks but instead their closest living relatives - are an extraordinarily rare sighting. Actually, it was just a few months ago, when a ghost shark was filmed alive in a natural habitat for the first time! The new species is the second largest ever recorded, and the 50th species of ghost shark so far.

Also known as chimaeras, rat fish, spook fish and rabbit fish, ghost sharks have been around since before the dinosaurs, having branched off from sharks nearly 400 million years ago and have remained isolated ever since. Researchers put the new species into the Hydrolagus genus, which basically means water rabbit. "(In Greek, "hydro" means "water" and "lagus" means "rabbit" or "hare.") The species was named this way because it has an interesting set of teeth that can only be described as buckteeth. As for the species name "erithacus", it is the genus name for robin birds in honor of Robin Leslie of the South African Department of Agriculture, Forestry and Fisheries, who helped Walovich study the ghost shark.

So far, the genus contains three other species, all found in the same area with H. erithacus between South Africa and Antarctica in the southeastern Atlantic and southwestern Indian Oceans. These species are H. africanus, H. mirabilis and H. cf. trolli

Basic anatomic illustration of Hydrolagus erithacus
An illustration of Hydrolagus erithacus showing the creature's pectoral fins, used to propel itself forward.

Fishermen who accidentally catch ghost sharks on a semi-frequent basis, have been saying for years that H. erithacus individuals didn't look like the other known ghost sharks.

"The scientists and the fishermen in South Africa knew this was not the same species because Hydrolagus africanus [another ghost shark in the same genus] is small, it’s brown, and this one was huge and really dark in color. Just visibly, they were definitely different species." Kristin Walovich, a graduate student at the Pacific Shark Research Center and main author of the study.

The abstract of the study describing the new species reads:

A new species of chimaerid, Hydrolagus erithacus sp. nov., is described from nine specimens collected from the southeast Atlantic and southwest Indian oceans from depths of 470–1,000 meters. This species is distinguished from all other Hydrolagus species based on the following characteristics: head bulky, relatively large, followed by stocky body; head and body height from about pectoral fin origin to pelvic fin origin similar, then tapering rapidly to filamentous tail; first dorsal fin spine height about equal to, or slightly less than first dorsal fin apex height; second dorsal fin up to 81% of total body length and uniform in height; trifurcate claspers forked for approximately 20% of total length; robust frontal tenaculum nearly uniform in width, prepelvic tenaculae with five to seven medial spines, and a uniform black coloration with robust, non-deciduous skin. Comparison of mitochondrial NADH2 gene sequences with other morphologically similar Hydrolagus species suggests that H. erithacus is a distinct species.

- Walovich KA, Ebert DA, & Kemper JM (2017). Hydrolagus erithacus sp. nov. (Chimaeriformes: Chimaeridae), a new species of chimaerid from the southeastern Atlantic and southwestern Indian oceans. Zootaxa, 4226 (4) PMID: 28187604

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