The largest subclass of the class Bivalvia in the phylum Mollusca. Eulamellibranchs are ciliary filter feeders with greatly enlarged ctenidia, in each of which the elongated gill filaments are held together in parallel series to form folded lamellae. The 30,000 living species constitute the most successful of molluscan groups, in terms both of individual numbers with their biomass and of ecological bioenergetics (calorie transfer in food chains).