Frilled Shark

Overview

The Frilled Shark (Chlamydoselachus anguineus), celebrated across paleontology and ichthyology as one of the most remarkable ‘living fossils’ on planet Earth, is an ancient, primitive deep-sea elasmobranch belonging to the order Hexanchiformes. Tracing an unbroken evolutionary lineage back over 80 million years to the Cretaceous period, this serpent-like predator resembles a mythological sea monster: possessing an elongated, chocolate-brown eel-like body, six pairs of frilly, collar-like gill slits, and an exceptionally wide terminal mouth armed with over 300 needle-sharp, trident-shaped teeth.

Operating as an efficient ambush predator along outer continental slopes and submarine canyons, Chlamydoselachus anguineus navigates deep oceanic trenches where it hunts slippery deep-sea squid and benthic teleosts. Unlike modern sharks whose jaws are located beneath a protruding snout, the frilled shark’s jaws are situated at the very tip of its skull, allowing it to open its mouth to an astonishing width and swallow soft-bodied cephalopods more than half its own length whole. Exhibiting the longest known gestation period of any vertebrate on Earth—lasting up to an astonishing 3.5 years—it maintains deep-water populations evaluated as Least Concern on the IUCN Red List.

Biology and Physical Characteristics

The anatomical construction of Chlamydoselachus anguineus preserves numerous ancestral elasmobranch features that have remained virtually unchanged since prehistoric eras: its skeleton is composed of poorly calcified, highly flexible cartilage, and its notochord is unsegmented, giving the shark the undulating swimming locomotion of an eel. Its gills feature six distinct pairs of gill openings with fleshy, ruffled red margins—the first pair joining completely across the throat to form a distinctive Elizabethan-style collar. Inside its terminal jaws are 25 rows of approximately 300 backward-curving teeth, each tooth bearing three sharp, pronged cusps (tricuspid) that interlock like rows of barbed wire; this dental architecture ensures that once a slippery, gelatinous squid is seized, escape is physically impossible. Its skin is embedded with small, abrasive dermal denticles, and its lateral line system is an open, unroofed groove—a primitive sensory trait that maximizes detection of faint acoustic pressure waves in the pitch-black abyss.

Behavior and Ecology

Frilled sharks are solitary, sluggish swimmers that spend most of their time hovering just above muddy continental shelf bottoms or navigating mid-water trenches. Because their long, slender bodies and tiny, posterior fins provide poor cruising endurance, they rely on sudden, explosive strikes: when tracking deep-sea squid, the shark bends its body into an S-shaped coil like a striking serpent, launching itself forward with a sudden flick of its paddle-like caudal fin, snapping its jaws forward to engulf the prey. Reproduction is aplacental viviparous (ovoviviparous): developing embryos remain inside the female’s body sustained entirely by internal egg yolks, requiring an extraordinary gestation period of approximately 42 months (3.5 years)—more than four times longer than a human pregnancy—driven by near-freezing temperatures and glacial metabolic rates in the deep sea.

Conservation and Human Impact

Chlamydoselachus anguineus is evaluated as Least Concern on the IUCN Red List, having been downlisted from Near Threatened due to its vast circumglobal geographic range and low interaction rates with industrial fisheries. Because it dwells at depths between 150 and 1,500 meters, it is rarely encountered; however, individuals are occasionally captured as incidental bycatch in deep-sea bottom trawls, gillnets, and longline fisheries targeting deep-water teleosts in Japan and the eastern North Atlantic. Captured specimens are rarely utilized commercially and are typically discarded as bycatch. Marine protected areas encompassing deep submarine canyons help buffer populations against deep-sea trawling impacts.

Interesting Factoid

The frilled shark has the longest pregnancy of any vertebrate animal on planet Earth, carrying its developing embryos inside its body for an astonishing three and a half years (42 months) before giving birth.