The macroalga Bosworthia from the Cambrian Burgess Shale and Kaili biotas of North America and China

• The first detailed descriptions are provided for two species of macroalgae from the Burgess Shale.
• A new Cambrian macroalgal genus, Walcottophycus, is erected.
• Most Chinese specimens previously assigned to Bosworthia are placed in Walcottophycus.
• It is concluded that Bosworthia currently is not known from China.
• The affinities of Bosworthia and Walcottophycus within the algae are evaluated.

A comprehensive restudy of all material assigned in previous reports to the noncalcified macroalgal genus Bosworthia Walcott from the Burgess Shale Formation (Cambrian Stage 5) of western Canada and the slightly older Kaili Formation of South China, together with investigation of previously unpublished material, indicates important morphological differences between the two species heretofore included within the genus. On the basis of these differences, B. gyges is removed from the genus and assigned to Walcottophycus gen. nov. Most specimens previously assigned to Bosworthia from the Cambrian of China, including those assigned to B. simulans Walcott, are transferred to W. gyges, and it is concluded that Bosworthia remains unknown in China. Morphological details for this material when evaluated in the context of molecular clock studies and other fossil macroalgae indicate that B. simulans may belong to the extant red algal subclass Rhodymeniophycidae (Florideophyceae) and indicate that W. gyges may be an early form of bryopsidalean alga within the Chlorophyta.