Hemiarthrum setulosum is a species of chiton in the family Hanleyidae, the only member of the genus Hemiarthrum. This chiton has an incomplete lateral tract in the nerve ring. They are the only knowwn species to have an incomplete one.
This is an epibiotic species, found on hard substrata including holdfasts of Macrocystis, cobbles encrusted with calcareous red algae and in mussel beds. This species feeds on red and green algae. It is highly sensitive to desiccation and intolerant to high salinities.