The frilled shark has been called everything from a "sea serpent" to a real-life "Loch Ness Monster" over the years in places where it lives, such as southeast Australia, New Zealand, Southeast Asia, West Africa, Chile and the Caribbean. A more accurate nickname is "the living fossil," since this shark belongs to a primitive species that has changed very little over millions of years.
Anatomy — When open, the frilled shark's mouth reveals 300 trident-shaped teeth aligned in 25 rows. Aside from its unmistakable toothiness, the mouth looks larger than that of other sharks because its jaws terminate at the back of the fish's head instead of underneath the skull. The head appears to be all mouth, capped off at the throat region with six frilled gills, hence its name.
The first gill slit cuts right across the throat, making it look as if someone sliced it with a knife there. The rest of the brown body is nearly identical to that of an eel, save for the elasmobranch's small pectoral fins, dorsal fin, anal fin and lengthy caudal fin. Because of the fin placement and shape, R. Aidan Martin of the ReefQuest Center for Shark Research once described the shark's posterior as looking like "the wings on a throwing dart."
Behavior — Because the frilled shark bears such a striking resemblance to an eel, ichthyologists once assumed it navigated the water by wriggling. Now it's known that this species possesses an oil- and hydrocarbon-packed liver that enable it to float and hover at depths between 160 and 660 feet. Although no one has ever observed the shark hunting, scientists theorize that the frilled shark strikes suddenly at its prey, more similar to a snake than an eel attack. It's also believed that the shark feeds in caves and crevices on continental slopes, perhaps explaining its thin and narrow physique.
Analysis of the shark's stomach contents suggests its diet consists of 61 percent cephalopods, a class of marine mollusks that includes squid, cuttlefish and octopus. These are some of the world's slipperiest creatures, which probably explains the shark's fork-like teeth. It takes all 300 of them to sink into the incredibly smooth skin of their chosen prey. Frilled shark also feed on other sharks when such opportunities arise. One Japanese specimen, for example, was documented as having a catshark in its stomach.
Reproduction and Threats — Many sharks undergo long gestation periods, but the frilled shark could actually break the world's record. Although research on this matter is still ongoing, scientists suspect frilled sharks could gestate for up to three and a half years. An average litter consists of six pups, many of which may not survive into adulthood; thus reproduction in the shark's deep-sea habitat is slow at best. Since temperatures are also colder at such levels, its metabolic cycle is thought to be equally sluggish.
Even after modern humans put a dent in the populations of certain sea dwellers, frilled sharks thrived, since fishermen rarely trawled near the seafloor. With the advent of fishing equipment that goes from 400 to 4,200 feet below the water's surface, captures of this shark as by-catch have sadly become more common in recent decades. Populations of the fish also appear to be more vulnerable to disease now, perhaps due to pollution, habitat changes, climate change effects on water temperature and other stresses.
The recent capture near Tokyo hauntingly symbolizes the current state of this near-threatened species. Shortly after the marine park officials captured the shark, they filmed its other worldly-looking undulating body, swimming with mouth agape. As it turns out, this extremely rare footage recorded the shark's last moments of life. The disoriented and weakened individual died just a few hours afterward.