Cook’s Swellshark

Tiny little puffer shark

Cooks swellshark (Cephaloscyllium cooki) is a little-known species of catshark, belonging to the family Scyliorhinidae. It is found in the Arafura Sea at a depth of 732-984 feet. It is easily identified by the eight dark, pale-edged saddles along its grayish brown body and tail. Like other swellsharks, it can inflate itself with water (or air on land) to deter predators.



Family: Scyliorhinidae – Catsharks

Genus: Cephaloscyllium 

Species: cooki


Phylum– Chordata

Class– Chondrichthyles


Common NameGround Sharks

Family– Scyliorhinidae

Common NameCatsharks




Average Size and Length: The maximum known length of this species is 30 cm/11.8 inches.

Current Rare Mythical Sightings: Cook’s swellshark was described by Peter Last, Bernard Séret, and William White in a 2008 Commonwealth Scientific and Industrial Research Organization (CSIRO) publication. It is named in honor of the late shark fishery biologist and conservationist Sid Cook. The type specimen is a 29 cm/ 11 inches long adult male collected from the Arafura Sea.

Teeth and Jaw: The long, narrow mouth does not have furrows at the corners and contains 50–61 tooth rows in the upper jaw and 49–62 tooth rows in the lower jaw. Each tooth has a long central cusp and a pair of smaller lateral cusps near the symphysis of the upper jaw. The upper teeth are exposed when the mouth is closed.

Head: It has a short, broad head. The head height is between 10.5-14.2% of the total length. The snout is flattened and rounded, with the nostrils preceded by laterally enlarged flaps of skin that do not reach the mouth. The snout-vent length is short, between 45.4-49.3% of the total length. They have wide nostrils; the width is between 3.0-3.4% of the total length. The eye-spiracle space is wide, between 1.0-1.2% of the total length. The slit-like eyes are positioned high on the head and followed by tiny spiracles. The prenarial is between 4.9-5.5% of total length, in length. The preorbital snout length is between 1.3-1.6 times the prenarial length.  

Denticles: The dermal denticles are widely spaced, with three points and a median ridge. The back is without greatly enlarged denticles.

Tail: The caudal fin is low, with a distinct lower lobe and a strong ventral notch near the tip of the upper lobe. The caudal peduncle is long.

Demographic, Distribution, Habitat, Environment and Range: Cook’s swellshark is found in the Arafura Sea from the Northern Territory of Australia to the Tanimbar Islands of Indonesia, at a depth of 732–984 feet. They are considered tropical benthopelagic.

Ram-Suction Index: More than likely they are high on the suction index.

Aesthetic Identification: Cook’s swellshark is a stalky-bodied shark, and can be identified by the eight dark, pale-edged saddles along its grayish brown body and tail. The dorsal coloration is distinctive, consisting of a grayish brown background with six pale-edged dark saddles along the body and two on the tail. The first saddle is curved forward, with its front edge intersecting each eye. There are pale dots on the snout and fins, and inside the saddles on the body. On the flanks, the dorsal coloration fades into the plain light gray of the ventral side. The fourth and fifth pairs of gill slits lie over the pectoral fin bases and are shorter than the first three. The pectoral fins are small and angular, with nearly straight trailing margins. The two dorsal fins have rounded apices. The first dorsal fin is much larger and taller than the second dorsal fin, originating over the back half of the pelvic fin bases, while the second is positioned opposite the similarly-shaped but slightly larger anal fin. The anal fin is low and at between 2.8-3.4% of the total length. It is 2.5-3.1 in prepectoral length, and 5.5-6.6 in prepelvic length. The pectoral fins are small, the height is between 9.4-10.2% of the total length. The posterior margin is between 8.9-9.8% of the total length. The pelvic fins are small and angular. Males have very long claspers; its outer length to at least 10% of the total length, almost reaching anal fin. The trunk width is between 17.1-21.7% of the total length. The anal-caudal space is between 6.3-6.9% of the total length.

Biology and Reproduction: They are more than likely oviparous. The vertebral centra is between 101-106.

Behavioral Traits, Sensing and Intelligence: Like other members of its genus, Cook’s swellshark can inflate its stomach with water (or air on land) to attempt to deter potential threats.

Speed: They are more than likely sluggish.

Cook’s Swellshark Future and Conservation: There is not enough data to evaluate.

Cook’s Swellshark Recorded Attacks on Humans: Not a threat to humans.