The frilled shark is considered a living fossil, because of its primitive, anguilliform (eel-like) physical traits, such as a dark-brown color, amphistyly (the articulation of the jaws to the cranium), and a 2.0 m (6.6 ft)–long body, which has dorsal, pelvic, and anal fins located towards the tail.

When hunting food, the frilled shark curls its tail against a rock and moves like an eel, bending and lunging to capture and swallow whole prey with its long and flexible jaws, which are equipped with 300 recurved, needle-like teeth.

In contrast to Garman's thesis, the ichthyologist Theodore Gill and the paleontologist Edward Drinker Cope, suggested that the frilled shark's evolutionary tree indicated relation to the Hybodontiformes (hybodonts), which were the dominant species of shark during the Mesozoic era (252–66 mya); and Cope categorized the Chlamydoselachus anguineus species to the fossil genus Xenacanthus that existed from the late Devonian period to the end of the Triassic period of the Mesozoic era.

[11] Nonetheless, the systematic biologist Shigeru Shirai proposed the Chlamydoselachiformes taxonomic order exclusively for the C. anguinesis and the C. africana species of frilled sharks.

However, in the late 2000s a large capture was made over an underwater seamount of the Mid-Atlantic Ridge, hauling in over 30 frilled sharks.

The mass capture of a wide variety of male and female specimens emphasized these seamounts as a location for the mating of the species.

[4][14] Frilled sharks are able to open jaws and devour food sources that are considerably greater than that of their size, this is a physical trait that is present in gulper eels and viperfish.

[4] The underside of the shark's eel-like body features a pair of long, thick folds of skin, separated by a groove, which run the length of the belly; the function of the ventral skin-folds is unknown.

[15][22] A cartilaginous skeleton and a large liver (filled with low-density lipids) are the mechanical means with which the frilled shark controls and maintains its buoyancy in the deep waters of the ocean.

[16] In New Zealand, the Takatika Grit, in the Chatham Islands, yielded frilled-shark, bird, and conifer-cone fossils that dated to the time of the Cretaceous–Paleogene boundary (66.043 ± 0.011 mya)[26] which suggested that the sharks lived inland, in shallow bodies of water far from the ocean.

The shallow-water frilled shark had larger, stronger teeth, suitable for eating mollusks; scarcity and plenty of food are indicated in the tooth's morphology of sharper points (cusps) oriented into the mouth.

[15] The high tendency to primarily consume the squids in their habitat can be supported by the frequent observation of beak remnants left behind during digestive processes.

[1] The mature female shark has two ovaries and a uterus, which is in the right side of her body; ovulation occurs fortnightly; and pregnancy ceases vitellogenesis (yolk formation) and the production of new ova.

[16] Both ovulated eggs and early-stage shark embryos are enclosed in chondrichthyes, ellipsoid egg-cases made of a thin, golden-brown membrane.

The frilled-shark embryo is 3.0 cm (1.2 in) long, has a pointed head, slightly developed jaws, nascent external gills, and possesses all fins.

This leads to some studies suggesting that the terminal position of their mouth, due to anterior elongation of the jaw, is a derived trait instead of ancestral.

[2] In pursuit of food, the frilled shark usually is a bycatch of commercial fishing, accidentally caught in the nets used for trawl-, gillnet-, and longline-fishing.

[1] In 2018, the New Zealand Threat Classification System identified the frilled shark as an animal "At Risk — Naturally Uncommon", not easily found living in the wild.