Scanning electron micrographs of the ctenidium of Thyasira sarsi; A gross transverse section, B longitudinal section of ventral portion of inner demibranch, C ciliated frontal surface, D transverse section through the frontal zone. E frontal surface with cilia removed. Figure 2F “Conchocele” excavata, longitudinal section of ventral portion of inner demibranch. abs abfrontal surface; fc frontal cilia; lc lateral cilia; lfc lateral frontal cirri; ifj inter filamental junction; ils inter lamellar septum; sbc supra branchial chamber.