1) Ceras 2) Ctenidium 1) Gill 2) Respiratory organ 
• (n.) A gill; a respiratory organ for breathing the air contained in water, such as many aquatic and semiaquatic animals have.
Bran'chi·a noun ; plural Branchiæ [ Latin , from Greek ..., plural of ....] (Anat.) A gill; a respiratory organ for breathing the air contained in water, such as many aquatic and semiaquatic animals have. 
Type: Term Pronunciation: brang′kē-ă, -ē Definitions: 1. The gills, or organs of respiration, in water-living animals.
Greek = gills, adjective - branchial.