It can be identified by its dorsal coloration, consisting of seven brown "saddles" and extensive darker mottling on a light tan background.

This species has often been confounded with the draughtsboard shark (C. isabellum) and the Sarawak pygmy swellshark (C. sarawakensis) in scientific literature.

American ichthyologists David Starr Jordan and Henry Weed Fowler described the blotchy swellshark in a 1903 volume of Proceedings of the United States National Museum, based on a 98 cm (39 in) long stuffed dry skin originally obtained from Nagasaki, Japan.

They gave it the specific epithet umbratile (from the Latin umbratilis, meaning "shaded") and assigned it to the genus Cephaloscyllium.

[4] The holotype dried skin could not be located when shark expert Stewart Springer prepared his 1979 review of the catsharks, and in its absence he synonymized C. umbratile with C. isabellum on the basis of "inconclusive morphometric differences".

Recently, the holotype was found again, and in 2008 Cephaloscyllium umbratile was re-described as distinct from C. isabellum by Jayna Schaaf-Da Silva and David Ebert.

[4] The blotchy swellshark is known to inhabit the northwestern Pacific Ocean from Hokkaido, Japan southward to Taiwan, including the Yellow Sea.

The snout is proportionately long and rounded, with large nostrils divided by short, triangular flaps of skin in front.

The small, horizontally oval eyes are placed high on the head and equipped with rudimentary nictitating membranes (protective third eyelids).

The caudal fin is large and broad, with the upper lobe longer than the lower and bearing a prominent ventral notch near the tip.

[4][7] Like other members of its genus, when threatened the blotchy swellshark is capable of rapidly inflating its stomach with water or air.

Cephalopods, mostly the squid Doryteuthis bleekeri and the cuttlefish Sepia spp., are also frequently taken, while crabs, shrimp, and isopods are occasionally consumed.

When the embryo is 11 cm (4.3 in) long, the external gills have been lost, the dermal denticles have begun to develop, and light brown saddles are present.

[8] From a series of captive rearing experiments, Sho Tanaka reported that hatchling sharks grew in length by up to 0.77 mm (0.03 in) per day.