†Calathium Billings 1865 (green alga)
Chlorophyceae - Receptaculitidae
Parent taxon: Calathida according to S. B. Church 1991
Sister taxa: none
Subtaxa: Calathium formosum, Calathium yersini
Type: Calathium formosum
Ecology: stationary epifaunal "photoautotroph"