鰓 - gills, gill slits

gills; branchia

gill slit

branchial arch; gill arch

gill plate; branchial plate; gill lamella; branchial lamella

prosobranchs

elasmobranchs

pterobranchs (hemichordates of class Pterobranchia)

enteropneusts (hemichordates of class Enteropneusta)

sea pen (any coelenterate of the family Pennatulidae or related families); sea feather

gill lamella; branchial lamella; gill filament

nudibranchs

gill sac; branchial sac; branchial pouch; inner branchial groove; pharyngeal pouch