a–e The ctenidium of Benthomodiolus lignocola a gross anatomy, b SEM of whole filaments, c SEM of inter filamentar junction, d SEM of tip of filament, e SEM of polygonal surface of microvilli (Knudsen 1970). Figures 4f–h. The ctenidium of B. geikotsucola. f SEM of a whole filaments gross anatomy, g SEM of inter filamentar junction, h SEM of the polygonal surface.