Its shell was long and conical, with the open end protected by an operculum, from which two fleshy arms called helens protruded at the sides.

These arms served to elevate the opening of the shells above the sea floor, acting like stilts.

[2] It is distinguished from Hyolithes by the presence of a longitudinal septum on the middle of the inner surface of the top of the shell.

A pair of wide structures of uncertain function extend along the length of the conical shell.

[2] The soft anatomy of Haplophrentis was key to establishing the hyoliths as members of the Lophophorata, the group containing brachiopods and phoronids.