The frilled shark, Chlamydoselachus anguineus, is a rarely seen deep-sea inhabitant often referred to as a “living fossil” because its appearance has changed little over millions of years. This elusive species belongs to the Hexanchiformes order, a group of sharks characterized by having six or seven gill slits, setting them apart from most modern shark species that possess only five. Known for its dark, eel-like body and primitive features, the frilled shark spends most of its life in the cold, dark waters of the continental slopes, making encounters with humans extremely infrequent.
Dimensions and Physical Measurements
Frilled sharks are considerable in size for an eel-like deep-sea fish, with adult females generally reaching larger sizes than males. The maximum recorded length for a male frilled shark is approximately 1.7 meters (5.6 feet), while females can grow to nearly 2.0 meters (6.6 feet) in total length. This difference in maximum size is a clear example of sexual dimorphism. Male frilled sharks typically attain sexual maturity at a length between 1.0 and 1.2 meters, whereas females reach maturity at a slightly greater length, ranging from 1.3 to 1.5 meters. The frilled shark’s slender, serpentine body contrasts sharply with the bulkier, torpedo-shaped build of most other sharks of similar length. The overall length is the most consistent measurement used for this species.
Anatomy and Deep-Sea Adaptations
The frilled shark’s morphology is highly specialized, starting with the six pairs of gill slits that give the species its common name. These gills possess ruffled edges, and the first pair is notably continuous across the throat, forming a distinctive collar-like structure. This unusual gill arrangement, combined with a dark, chocolate-brown coloration, contributes to the shark’s reputation as a creature from a prehistoric era.
Its body is slender and flexible, resembling that of an eel, which is a form known as anguilliform. The single dorsal, pelvic, and anal fins are all situated far back on the body, close to the tail. This posterior location is believed to assist with propulsion and maneuverability in the water column.
Deep-sea living necessitates buoyancy adaptations, which the frilled shark achieves through a reduced, poorly-calcified skeleton and an enormous liver filled with low-density lipids. The shark’s wide mouth is positioned terminally, at the very front of its flattened, snake-like head, rather than underneath like most sharks. This mouth contains rows of needle-sharp teeth, numbering up to 300 in total. Each tooth is distinctive, featuring three slender, backward-pointing cusps, a unique structure that efficiently hooks and secures the slippery bodies of deep-sea prey.
Habitat and Hunting Behavior
The frilled shark has a broad but patchy global distribution, found in both the Atlantic and Pacific Oceans, typically over the outer continental shelves and upper slopes. While it has been caught at depths as deep as 1,570 meters (5,150 feet), the majority of specimens are found in the bathypelagic zone, usually between 500 and 1,000 meters, where light penetration is minimal. This deep-water environment is characterized by cold temperatures and low food availability, which influences the shark’s slow-moving lifestyle.
The hunting behavior of the frilled shark is believed to be based on ambush predation, utilizing its flexible body to strike at passing prey. Unlike faster-swimming, pelagic sharks, the frilled shark often moves with a slow, serpentine motion, similar to a sea snake or eel. When attacking, it can open its jaws exceptionally wide, allowing it to engulf prey that can be more than half its own length. Its diet primarily consists of deep-water squid, along with bony fish and smaller sharks. Observations have suggested that the contrasting white color of its teeth against the dark ocean background may even serve as a lure for curious prey in the abyssal darkness.