Heterorotula lucasi sp. nov. from the Pigeon River, Tennessee (type locality). Micrographs of gemmular theca cross sections by SEM A theca with the radial monolayer of short and long spiny birotules bearing crenulated/notched margins of rotules. proximal, partly overlapping, rotules adherent to the multilayered inner layer (cross section, outer layer, and pneumatic layer not evident) B trilayered theca with short and long spiny birotules embedded in the fibrous/chambered pneumatic layer in between the smooth outer layer and the multilayered inner layer, C radial birotules in the fibrous to chambered pneumatic layer D proximal rotule with crenulated/notched margins adherent to the multilayered inner layer surrounding the central gemmular cavity containing totipotent cells. Scale bars: 100 μm (A); 50 μm (B); 30 μm (C); 20 μm (D).