No ctenidia but pallial branchiae in a circle between mantle and foot.
ctenidia, plural of Ctenidium: Gills, or breathing-organs, adapted to water-respiration.
Probably a straining of water from solid particles is effected by the lattice-work of the ctenidia or gill-plates.
A single pair of ctenidia (gill-plumes) is present instead of the two pairs in Nautilus.
Two pairs of ctenidia, and two pairs of renal tubes without reno-pericardial apertures.