Haplophrentis

Haplophrentis was a tiny shelled hyolithid which lived in the Cambrian Period. 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 probably acted as stabilisers, or were used for locomotion, rowing the animal across undersea mudflats.

Morphology
Haplophrentis ranged in length between 2–6 cm.[verification needed] 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.

Affinity
The hyolithids are thought to belong to the molluscan total-group, although this is uncertain.