The Coelosclerithophorans are a polyphyletic group of organisms bearing hollow sclerites made of aragonite, and with a supposedly distinctive microstructure.

The shells of this group and the molluscs appear to have originated in the same fashion.

[4] There are two groups within the coeloscleritophorans: the Sachitids, to which Halkieria and Wiwaxia belong, and the Chancellorids.

The Ediacaran fossil Ausia has been touted as an ancestral 'intermediate' between both of these groups.

[5] These are common constituents of Lower Cambrian small shelly fossil assemblages.