ctenidium: a comb-like structure occurring on any part of an insect.
No ctenidium, but a pulmonary cavity; operculum with an apophysis.
There is a ctenidium, except in some Thecosomata and Gymnosomata, and an osphradium.
Ctenidia, plural of ctenidium: Gills, or breathing-organs, adapted to water-respiration.
To the left of the ctenidium a pulmonary sac, separated from it by an incomplete septum, amphibious.
Mantle with two posterior appendages; ctenidium large and capable of protrusion from pallial cavity.
Cephalic shield continuous with dorsal integument; no shell; ctenidium projecting from mantle cavity.
Without shell and operculum, but with pallial cavity and ctenidium.