[4] Like all members of the genus Synodontis, S. membranaceus has a strong, bony head capsule that extends back as far as the first spine of the dorsal fin.

[6] All members of Syndontis have a structure called a premaxillary toothpad, which is located on the very front of the upper jaw of the mouth.

[6] On the lower jaw, or mandible, the teeth of Syndontis are attached to flexible, stalk-like structures and described as "s-shaped" or "hooked".

[6] The color of the fish is silvery grey or whitish on the back and sides, with the lower parts and underside dark brown to black.

Juveniles may have poorly defined dark blotches on the body and spots forming stripes on the fins that will fade with age.

[1] In captivity, however, the fish sometimes stops swimming upside down and its color pattern reverses, so that it is dark on the back and light on the underside.

[1] The reproductive habits of most of the species of Synodontis are not known, beyond some instances of obtaining egg counts from gravid females.