Scanning electron micrographs of the ctenidium of Conchocele bisecta; A frontal surface, openings of tubules arrowed; B frontal surface removed to reveal tubules; C abfrontal surface of laminar filaments; D longitudinal section; E edge of a frontal face; F section of the frontal face with projection on the inter filamentar junction arrowed. abf lam laminar abfrontal surface; fz frontal zone; ils inter lamellar space; ilj inter lamellar junction; lz laminar zone; tbz tubular zone.