The diversity of feeding structures in polychaetes can be classified into several functional categories. These feeding categories are not indicative of phylogenetic relationships but are useful for ecological purposes and were developed by Fauchald and Jumars (1979). The categories of Fauchald and Jumars have been slightly modifed here, and one, 'Bacterial symbiosis', has been added. As will be shown here, a given functional category can contain taxa with different buccal organs. While the survey we perfom will be basically phylogenetic, and so a review of the basic feeding structures, reference will be made to various ways that polychaetes use these structures to feed.

Raptorial feeding

This term refers to annelids that use their buccal apparatus, usually an eversible muscular ventral or muscular axial organ, to seize their food items. The two groups of polychaetes that have evolved jaws (Euncida and Phyllodocida) use them to either seize live animals (carnivores), tear off pieces of algae (herbivores) or to grasp dead and decaying matter (scavengers). Some of the raptorial groups such as Phyllodocidae appear to have lost their jaws and use their eversible proboscis to grasp prey. Members of the eunicid family Onuphidae, such as Australonuphis,are well known from Australian beaches. They are burrowing polychaetes that emerge where waves break to seek their prey. They have powerful jaws and feed on small to medium sized animals. Australonereis (Nereididae), an errant polychaete which builds a temporary tube in predominantly sandy habitats in sheltered habitats on the Australian east coast, feeds on algae, using its powerful jaws attached to the eversible pharynx for grazing.

Non-selective deposit feeders

Many types of annelid eat mud, sand or soil. The sediment is ingested and any digestible organic material is assimilated as it passes through the alimentary canal. This form of feeding is also called non-selective deposit feeding. The majority of groups using this method have a ventral buccal organ or simple axial pharynx. Of the polychaete groups that are non-selective deposit feeders some, such as arenicolids and maldanids, live in relatively permanent burrows or tubes and ingest the sediment in such a way that a continuous rain of sand or mud is falls in front of them to eat. Others such as opheliids, do not have permanent burrows or tubes but move about the sediment, eating it as they tunnel. The amount of nutritional value in sediment varies but shallow-water mud deposits tend to carry the largest numbers of non-selective deposit feeders. The total organic matter in such areas can be as low 1-2% and most of the deposit feeders have to eat continually. The processing time (from ingestion to passage through to the rectum) for the sediment can be as little as 15 minutes in taxa such as Arenicola.

Selective deposit feeders

Some deposit feeders do not ingest sediment haphazardly but use accessory feeding structures such as palps to aid them sort organic material from the sediment prior to ingestion. Selective deposit feeders generally live in tubes, though the method of sorting varies according to the types of palps that are present. In terebellids that live in vertical tubes the multiple palps are laid out over the sediment surface. Each palp has a longitudinal ciliated groove into which mucus is secreted. The palps are extended by 'creeping' on cilia and detritus is selected or rejected. The selected particles stick to the mucus and are carried along the groove by ciliary action to the base of the palp. Each palp is wiped periodically on the lower lip where cilia carry the mucus plus detritus into the mouth. Polychaetes with only a single pair of grooved palps, such as spionids, use a similar method of feeding, sweeping the palps over the sediment surface or waving them in the water column to gather food.

Filter feeders

A number of polychaete groups have the ability to collect particles suspended in the water column. All known filter-feeders live in some sort of tube. The best-known are Sabellidae and Serpulidae (feather duster worms) and the Chaetopteridae (parchment-tube worms). Sabellids and serpulids have elaborate palps forming a radiolar crown. When the crown is expanded out of the tube a funnel is formed. The cilia beat and create a current in the surrounding water. This current passes through the tentacles into the funnel and swirls around the base of the funnel and then upwards and outwards. Food particles are trapped on the pinnules and carried into the groove by cilia. The ciliary current carries the particles towards the base of the radioles where the material is sorted. Small particles are swallowed while large ones are pushed away from the mouth and drop into the water. Some of these worms sort the particles into three sizes, with mid-sized particles being used in the construction of the tube.

Bacterial Symbiosis

This form of nutrition means that the polychaete has no need to ingest food matter. Instead they rely on the presence of chemoautotrophic bacteria that live in their bodies to provide them with their nutritional requirements. This is similar to the association of zooxanthellae with corals. The most famous example of this form of symbiosis in Annelida occurs in Siboglinidae. This group was formerly treated as the phyla Pogonophora and Vestimentifera until the cladistic analyses of Rouse and Fauchald (1997). The mode of nutrition in this group was the subject of debate for many years since they were said to lack a gut. Siboglinids live in areas where there is a high level of reduced-sulphur or methane in the water or sediment around their tubes. There is now considerable evidence that most, if not all, of their nutritional requirements are derived from the bacteria in the body, which can make up 15% of the animal's total body weight. Large taxa, such as those in Riftia, live around deep-sea hydrothermal vents from which heated water, sulfide and carbon dioxide are ejected. The palps of siboglinids project from the tube and are richly supplied with blood vessels that serve for the respiratory purposes of the worm, but also to transport the sulphide and carbon dioxide that are needed by the symbiotic bacteria.

We will now proceed through the various kinds of buccal organs that are found among polychaetes and relate them to the feeding mechanisms they are employed for.