a-d Late stage of morphogenesis (a, b) and middle stage of reorganization (c, d) in Heterogastrostyla salina nov. spec. after protargol staining. a, c Ventral views to show the development of the oral primordium, fronto-ventral-transverse anlagen and marginal rows anlagen, arrow in (c) depicts the anlage for the left marginal row. b, d Dorsal views to show the development of dorsal kineties and nuclear apparatus, arrowheads in (b) indicate the newly differentiated caudal cirri. DMA, dorsomarginal anlage; Ma, macronuclear nodules; Mi, micronuclei; OP, oral primordium; RMA, anlage for the right marginal row; 1−3, dorsal kineties anlagen 1−3. Scale bars = 50 μm (a, b); 40 μm (c, d).