Species of the family Moniliformidae are usually pseudosegmented and have a cylindrical proboscis with longitudinal rows of hooks that have posteriorly directed roots.

Moniliformidae are further characterized by the presence of a simple, double-walled proboscis receptacle with the outer wall having spirally aligned muscle fibers (with the exception of Australiformis), brain at posterior end of receptacle, and dorsal and ventral lacunar canals.

[4] The cerebral ganglion is in the mid to posterior region, and the lemnisci are long and flat and not bound to the body wall.

These worms also lack protonephridia and males have eight cement glands, each with a giant nucleus, which are used to temporarily close the posterior end of the female after copulation.

[2] Its body consists of a proboscis armed with hooks which it uses to pierce and hold the gut wall of its host, and a long trunk.

[2] Infestation of marsupials by A. semoni may cause debilitating inflammation of the stomach (gastritis) with granulomatous ulcers.

[13] The genus Promoniliformis Dollfus and Golvan, 1963[14] is characterized by possessing two distinct kinds of proboscis hooks.