"M. pfefferi" is a robust-looking species, having a very broad, oval mantle. Arms are broad and blade-like and have four rows of suckers. The modified arm used by males for fertilisation, called the hectocotylus, is borne on the left ventral arm. The oral surface of the modified region of the hectocotylus is wide, swollen, and fleshy. It bears transversely grooved ridges and a deep furrow running along the middle. The sucker-bearing surface of the tentacular clubs is flattened, with 5 or 6 suckers arranged in transverse rows. These suckers differ greatly in size, with the largest located near the centre of the club. Three to four median suckers are especially large, occupying most of middle portion of the club. The swimming keel of the club extends considerably near to the carpus. The dorsal and ventral protective membranes are not joined at the base of the club, but fused to the tentacular stalk. Dorsal and ventral membranes differ in length and extend near to the carpus along the stalk. The dorsal membrane forms a shallow cleft at the junction with the stalk. This particular species of cuttlefish is the only one known to walk upon the sea floor. Due to the small size of its cuttlebone, it can float only for a short time.