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What the sources say

Frilled SharkChlamydoselachus anguineus

Every figure, record and mechanism on the Frilled Shark profile was written from a source, and this is the working table behind it: 51 claims checked word for word against these sources. The left column is what the page says. The right column is the source's own words, copied, not paraphrased; a ... marks a cut and[brackets] an insertion. Open any source and check it yourself.

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Source
01

Animal Diversity Web, University of Michigan

Chlamydoselachus anguineus (frill shark). Animal Diversity Web, University of Michigan.

The page saysA slow-swimming
The source saysThey are among the slowest of shark species (Parker & Parker, 1999).
The page sayssix-gilled deep-sea shark
The source sayshas six gill openings (most sharks have five)
The page saysusually chocolate brown
The source saysThe body tends to be a chocolate brown color.
The page saysMost sharks breathe through five gill slits. This one has six
The source saysChlamydoselachus anguineus has six gill openings (most sharks have five)
The page saysThis one has six, each edged with a frilly margin of skin, which is how it got its name.
The source saysChlamydoselachus anguineus has six gill openings (most sharks have five). The first gill is continuous across the throat, while all the gills are surrounded by frilly margins of skin-hence the name "frilled shark."Note: "which is how it got its name" paraphrases "hence the name"
The page saysThe teeth on both jaws each carry three long, sharp points
The source saysThe teeth are alike both on the upper and lower jaws, with three elongate, sharp cusps separated by two intermediate ones
The page saysThe frilled shark is among the slowest of shark species
The source saysChlamydoselachus anguineus is a slow-moving, deep water shark. They are among the slowest of shark species (Parker & Parker, 1999).
The page saysFew of its predators are known, though other sharks are thought likely to take it.
The source saysThere are few known predators of frilled sharks. Other sharks are likely predators
The page saysPeople sometimes catch it too, by accident, when bottom trawls or nets pull it up.
The source sayshumans may take these sharks incidentally as fishing bycatch. Becauses they occupy the benthos, they are sometimes caught during bottom trawling or in nets when they venture near the surface
The page saysdangerLevel: Medium
The source saysThese are not dangerous sharks, but their teeth have lacerated the hands of the unwary scientist and or fisherman examining or holding them.

Source
02

Finucci & Charles 2024

Finucci & Charles (2024). Chlamydoselachus anguineus. The IUCN Red List of Threatened Species 2024: e.T41794A124416882.

The page saysLeast Concern
The source saysIUCN Red List category: Least Concern (LC). Chlamydoselachus anguineus Garman, 1884, IUCN taxon 41794.Note: category read through GBIF's copy of the Red List, as the source pack instructs; the DOI is the assessment page itself

Source
03

López-Romero et al. 2020

López-Romero et al. (2020). Growth trajectories of prenatal embryos of the deep-sea shark Chlamydoselachus anguineus (Chondrichthyes). Journal of Fish Biology.

The page sayswhose pregnancy may run three and a half years
The source saysThe gestation period of C. anguineus is the longest period known for all vertebrates, lasting 3.5 years
The page saysand even smaller sharks
The source saysIt is considered a benthopelagic shark feeding on cephalopods, bony fish and even smaller sharks
The page saysa long, eel-like body
The source saysIt has an elongated, eel‐like body
The page saysgrows to an average total length of about 150 cm
The source saysit grows up to an average total length (TL) of 150 cm
The page sayswith the largest on record at 196 cm
The source sayswith a maximum reported TL of 196 cm (Gudger & Smith, 1933)
The page saysPregnant for Years
The source saysalthough the gestation period estimation can be as low as 1–2 years (Compagno, 1984; Gudger & Smith, 1933)Note: heading; every estimate, low (1-2 years) or high (3.5 years), is at least a year
The page saysgive birth to live young rather than laying eggs
The source saysFrilled sharks are aplacental viviparous with a year‐round mating and breeding season.Note: viviparous means live-bearing; "rather than laying eggs" is the definition
The page saysEmbryos hatch inside the mother's body at just 5.5 cm long
The source saysThey hatch within the mother's uterus when they reach a TL of 5.5 cm
The page sayskeep growing on their own yolk supply until they're born at 40 to 60 cm
The source saysremain there, feeding on their yolk sack until they are born at a TL of 40–60 cm
The page saysusually in litters of two to 10
The source saysUsually there are two to 10 embryos in each litter.
The page saysOne estimate puts the pregnancy at 3.5 years, which a 2020 study calls the longest gestation known for any vertebrate
The source saysThe gestation period of C. anguineus is the longest period known for all vertebrates, lasting 3.5 yearsNote: the 3.5-year figure is Tanaka et al. 1990, reported by this 2020 paper; 2020 is the reference's own year
The page saysother estimates run as low as one to two years
The source saysalthough the gestation period estimation can be as low as 1–2 years (Compagno, 1984; Gudger & Smith, 1933)
The page saysturned out in 2009
The source saysEbert and Compagno ( 2009 ) identified the populations around South Africa as separate species, Chlamydoselachus africana

Source
04

Tanaka et al. 2013

Tanaka et al. (2013). Evolutionary Relations of Hexanchiformes Deep-Sea Sharks Elucidated by Whole Mitochondrial Genome Sequences. BioMed Research International.

The page sayswhose lineage is estimated at 82 million years old
The source saysthe divergence time of C. anguineus is estimated as 82.0 Mya (78.1 Mya~87.9 Mya)
The page saysSix frilly gill slits, tricuspid teeth, and a lineage estimated at 82 million years old.
The source saysthe divergence time of C. anguineus is estimated as 82.0 Mya (78.1 Mya~87.9 Mya)Note: combined stats line; the gill/teeth parts reuse the adw-frilled-shark and record-2025 claims below
The page saysMitochondrial DNA analysis puts the frilled shark's own lineage at roughly 82 million years old
The source saysthe divergence time of C. anguineus is estimated as 82.0 Mya (78.1 Mya~87.9 Mya)Note: the paper's method is full mitochondrial-genome sequencing
The page saysbroadly matches the fossil record of its wider group, which goes back about 85 million years
The source saysThis estimation is largely consistent with the known fossil record of Chlamydoselachiformes (85 Mya)

Source
05

Indurain et al. 2025

Indurain et al. (2025). New record of Frilled shark Chlamydoselachus anguineus Garman, 1884 (Chondrichthyes: Hexanchiformes) in the South Pacific Ocean. PeerJ.

The page saysContinental slopes and outer shelves, usually at 120 to 1,500 meters, across the Atlantic and Pacific Oceans
The source saysThis species usually inhabits outer continental and insular shelves and continental slopes at depths of 120–1,500 m
The page saysa shape scientists call tricuspid
The source saysthe presence of tricuspid teeth
The page saysusually lives along outer continental shelves and continental slopes
The source saysThis species usually inhabits outer continental and insular shelves and continental slopes
The page saysFrilled sharks are rarely seen
The source saysAlthough rarely observed, frilled sharks have been documented as bycatch in trawl and bottom longline fisheries throughout its range
The page sayswith a wide-ranging but patchy distribution in the Atlantic and Pacific Oceans
The source saysC. anguineus has a wide-ranging but sporadic distribution in the Atlantic and Pacific Oceans
The page saysusually at depths of 120 to 1,500 metres
The source saysThis species usually inhabits outer continental and insular shelves and continental slopes at depths of 120–1,500 m
The page saysThey have been recorded as bycatch in trawl and bottom longline fisheries throughout their range.
The source saysfrilled sharks have been documented as bycatch in trawl and bottom longline fisheries throughout its range
The page saysworking the continental slopes usually 120 to 1,500 meters down
The source saysThis species usually inhabits outer continental and insular shelves and continental slopes at depths of 120–1,500 m

Source
06

Kubota, Shiobara & Kubodera 1991

Kubota, Shiobara & Kubodera (1991). Food habits of the frilled shark Chlamydoselachus anguineus collected from Suruga Bay, central Japan. Nippon Suisan Gakkaishi.

The page saysMostly squid, plus some fish
The source saysThe food items of this shark were mostly decapodan cephalopods and fishes, which were found at the frequencies of 60.5% and 10.5%, respectively among the stomachs containing food.Note: the cephalopods identified by beak were squid (Todarodes pacificus, Sthenoteuthis oualaniensis, Gonatus sp.)
The page saysStomach checks on 139 frilled sharks caught in Suruga Bay, Japan, between 1984 and 1988
The source saysa stomach content analysis of frilled shark Chlamydoselachus anguineus is presented based on 139 specimens caught incidentally by sergestid shrimp midwater trawling or bottom gill-net fishing conducted in Suruga Bay from 1984 to 1988
The page saysfound squid in most of the stomachs that held any food, and fish in some
The source saysThe food items of this shark were mostly decapodan cephalopods and fishes, which were found at the frequencies of 60.5% and 10.5%, respectively among the stomachs containing food.
The page saysNearly three-quarters of the sharks had empty stomachs
The source saysthe empty stomach rate of frilled shark stood as high as 73.4% throughout almost the year
The page saysan extremely high rate compared with other deep-water sharks
The source saysThe empty stomach rate of specimens examined was 73.4% showing an extremely high level as compared with other deep-water sharks.
The page saysThe 77 females in that sample weighed between 6.2 and 12.1 kg; the 62 males were smaller, between 3.2 and 5.7 kg
The source says77 females with a total body length ranging from 1,376 to 1,768mm and weighing between 6,230 and 12,120g, and 62 males with total body length ranging from 1,178 to 1,486mm and weighing between 3,234 and 5,740 gNote: kg figures are grams converted and rounded to one decimal
The page saysa 1,618 mm frilled shark caught off Choshi, Japan, had eaten a 590 g shark, Apristurus japonicus, reported as the first documented case of a frilled shark preying on another shark
The source saysTaniuchi8) reported that a frilled shark measuring 1,618mm in total length, from Choshi in Japanese coastal waters, preyed on an Apristurus japonicus of 590g, as the first documented case of predation on another shark by a frilled shark.

Source
07

Ebert & Compagno 2009

Ebert & Compagno (2009). Chlamydoselachus africana, a new species of frilled shark from southern Africa (Chondrichthyes, Hexanchiformes, Chlamydoselachidae). Zootaxa.

The page saysRare, Deep, and Split in Two
The source saysis now known to contain at least two speciesNote: heading; "two" refers to the anguineus/africana split covered below it; "Rare" is the record-2025 "rarely observed" claim
The page saysSharks from off southern Angola, Namibia and South Africa, long believed to be the same species
The source sayslong believed to be a monotypic family and genus, consisting of a single wide ranging species, Chlamydoselachus anguineus (Garman, 1884), is now known to contain at least two species
The page saysturned out in 2009 to differ on the inside: in the structure of the skull and in their vertebra, spiral valve and fin-cartilage counts. They were named a species of their own, Chlamydoselachus africana
The source saysThe new species, although difficult to distinguish externally from the well known C. anguineus, differ internally by the structural differences in the chondrocranium, lower total vertebral and spiral valve counts, and pectoral-fin radial counts. The new species, Chlamydoselachus africana, is known from off southern Angola, Namibia, and South Africa.Note: 2009 is the reference's own publication year; chondrocranium is the cartilage skull, pectoral-fin radials the fin cartilages

Source
08

Kobayashi, Tomonaga & Tanaka 1992

Kobayashi, Tomonaga & Tanaka (1992). Identification of a second immunoglobulin in the most primitive shark, the frill shark, Chlamydoselachus anguineus. Developmental & Comparative Immunology.

The page saysA 1992 study, which described it as "the most primitive extant shark"
The source saysisolated from serum of the frill shark, Chlamydoselachus anguineus, the most primitive extant sharkNote: 1992 is the reference's own publication year; the ranking is kept as that paper's description
The page saysfound two distinct classes of antibody in its blood serum, a five-unit IgM and a second class built as pairs and single units
The source saysWe thus concluded that the frill shark has two distinct classes of immunoglobulins: one a pentameric IgM and the other a second class of immunoglobulin with dimeric and monomeric structure.
The page saysThe authors called the second class of considerable interest for how the body recognises and removes foreign material.
The source saysThe presence of the second Ig is of considerable interest with respect to antigen recognition and exclusion.

Source
09

Goto & Hashimoto 1976

Goto & Hashimoto (1976). Studies on the teeth of Chlamydoselachus anguineus, a living archaic fish. Japanese Journal of Oral Biology.

The page saysA 1976 study of its teeth found their arrangement and shape closely resemble those of Cladoselache, a shark that swam during the Devonian period
The source saysIn the arrangement pattern and morphology of the teeth, Chlamydoselachus is very similar toCladoselache, a Devonian shark.Note: 1976 is the reference's own publication year; quote keeps the cached text's missing space
The page saysconcluded the frilled shark has one of the most primitive types of shark teeth
The source saysTherefore, it is considered that Chlamydoselachus has one of themost primitive shark teeth type.Note: quote keeps the cached text's missing space

How the table was made: a writer drafted the profile from these sources and logged each claim with its quote, a reviewer with nothing but this table checked every sentence said no more than its quote, and a script confirmed each quote appears word for word in the source. The method is in the site'sAbout page.