The visitor was first formally described as Membracidichthys elongatus by the Australian ichthyologist Gilbert Percy Whitley with the type locality given as the Tiflis Passage in Moreton Bay in Queensland.

[2] Whitley classified his new species in a new subgenus of Membracidichthys which was subsequently recognised as a valid monotypic genus Adventor.

[8] The visitor has a head with a low dorsal profile and a projecting chin and a mouth which does not reach to underneath the small eye.

This species has a compressed, long body which is bare of scales but which is densely covered in velvety warts extending to around the eyes.

There are small dark-brown eyespots on the top of the head, nape, and around the spiny part of the dorsal fin with vague brown spots along the inner rear edge of the gill slit.