Ghost Shark Chimaera First Time in Video

The odd-looking fish, which sports a retractable sex organ on its head, was also spotted in the Northern Hemisphere for the first time. Ghost sharks are dead-eyed, wing-finned fish rarely seen by people. Chimaeras are cartilaginous fishes in the order Chimaeriformes, known informally as ghost sharks, rat fish, not to be confused with the rattails, spookfish, not to be confused with the true spookfish of the family Opisthoproctidae, or rabbit fish, , not to be confused with the true rabbitfishes of the family Siganidae.Even though ghost sharks have been gliding through the depths since long before the dinosaurs, we still know very little about them. Now, video recently released by the Monterey Bay Aquarium Research Institute in California has shined new light on these mysterious creatures. At one time, a "diverse and abundant" group, based on the fossil record, their closest living relatives are sharks, though in evolutionary terms, they branched off from sharks nearly 400 million years ago and have remained isolated ever since. Today, they are largely confined to deep water.

Even though ghost sharks have been gliding through the depths since long before the dinosaurs, we still know very little about them. Now, video recently released by the Monterey Bay Aquarium Research Institute in California has shined new light on these mysterious creatures.

Chimaeras live in temperate ocean floors down to 2,600 m (8,500 ft) deep, with few occurring at depths shallower than 200 m (660 ft). Exceptions include the members of the genus Callorhinchus, the rabbit fish and the spotted ratfish, which locally or periodically can be found at relatively shallow depths. Consequently, these are also among the few species from the Chimaera order kept in public aquaria. They have elongated, soft bodies, with a bulky head and a single gill-opening. They grow up to 150 cm (4.9 ft) in length, although this includes the lengthy tail found in some species. In many species, the snout is modified into an elongated sensory organ.

Like other members of the class Chondrichthyes, chimaera skeletons are constructed of cartilage. Their skin is smooth and largely covered by placoid scales, and their color can range from black to brownish gray. For defense, most chimaeras have a venomous spine located in front of the dorsal fin. Chimaeras resemble sharks in some ways: they employ claspers for internal fertilization of females and they lay eggs with leathery cases. They also use electroreception to locate their prey. However, unlike sharks, male chimaeras also have retractable sexual appendages on the forehead (a type of tentaculum) and in front of the pelvic fins. The females lay eggs in spindle-shaped, leathery egg cases.
Tracing the evolution of these species has been problematic given the scarcity of good fossils. DNA sequences have become the preferred approach to understanding speciation.To find out its identity, the institute reached out to Ebert and other chimaera experts. The team analyzed the video and now believe it's a pointy-nosed blue chimaera, Hydrolagus trolli, a species usually found near Australia and New Zealand, according to a recent study in the journal Marine Biodiversity Records. Though the ghost shark is not new to science, it's still exciting: The video is the first time the pointy-nosed blue chimaera has been seen alive in its natural habitat. The order appears to have originated about 420 million years ago during the Silurian. The 39 extant species fall into three families – the Callorhinchids, Rhinochimaerids and Chimaerids with the callorhinchids being the most basal clade. The families appear to have diverged during the late Jurassic to early Cretaceous (170–120 Mya.)
 They also differ from sharks in that their upper jaws are fused with their skulls and they have separate anal and urogenital openings. They lack sharks' many sharp and replaceable teeth, having instead just three pairs of large permanent grinding tooth plates. They also have gill covers or opercula like bony fishes.