Sepia braggi, the slender cuttlefish, is a species of cuttlefish native to the Indo-Pacific Ocean. It has been found in coastal waters of southern Australia. This species was first collected in South Australia by its namesake, William Lawrence Bragg. Sepia braggi was then described by Sir Joseph Cooke Verco in 1907.Sepia braggi is part of the subgenus Doratosepion which contains to 41 species of cuttlefish in total.

Description Sepia braggi is a relatively small species of cuttlefish. Females of the species are larger than males and they grow to a mantle length of 80 mm and 49 mm, respectively. The mantle elongates to 3 times longer than it is wide. The mantle is cigar-shaped and triangular towards the anterior end. Narrow fins extend along the lateral margin of the mantle and widen along the posterior. The head is short and narrower than the mantle.