Heterorotula lucasi sp. nov. from the Pigeon River, Tennessee (type locality). Micrographs of gemmules by SEM A gemmule with multilayered theca armed by radial gemmuloscleres around the central cavity bearing a mass of totipotent cells B outer layer at theca surface with a few emerging rotules of gemmuloscleres, acanthoxeas of the cage and sligtly elevated foramen closed by a membrane C theca of an aged gemmule covered by diatoms frustules, surrounded by the spicular cage of acanthoxeas and outer layer with open foramen after hatching D theca with a fragment of spicular cage and outer layer armed by dense distal rotules of gemmuloscleres E fibrous structure of outer layer with sligtly elevated foramen closed by a membrane before hatching F fibrous structure of outer layer around foramen and sparse broken shafts of gemmuloscleres. Scale bars: 500 μm (C, D); 300 μm (A, B); 100 μm (E); 20 μm (F).