Deposit-feeding animals acquire food by swallowing large volumes of sediment. Possible food sources include organic debris and sediment-associated microbes. The relative importance of these classes of food is currently an area of active research. The idea that microbes attached to sediment and detritus particles constitute the major food source of deposit feeders is being replaced by more complex models that incorporate interactions between animals and the food sources in the sedimentary matrix. Many deposit feeders appear to require both microbial and detrital foods.