Polychaetes

The Polychaeta, with over 10,000 described species, is the largest class. They are all aquatic, with most living in marine or estuarine environments. The other classes, Oligochaeta (terrestrial and aquatic earthworms), Hirudinea (leeches) and Myzostomida are much less common in marine waters.

Many polychaetes live in burrows, either with or without tubes, underneath boulders, in crevices, on weed, in sand or on rock. Some are carnivores, others herbivores or scavengers and some are opportunistic omnivores, eating whatever comes their way. Many are filter-feeders that strain the water column for food particles, while some are deposit-feeders which ingest sediments to obtain nutrients from the algal and bacterial films that cover them. All of these different modes of life are represented in the polychaete collections from the three sites. Some of the more common polychaetes are described below.

The samples collected contained a large number of tube-dwelling, deposit-feeding polychaetes. These included representatives from the Ampharetidae, Terebellidae, Magelonidae, and Spionidae families. The tubes can take a number of forms. They may be permanent calcareous tubes, or semi-permanent tubes created of soft mucous to which is adhered particles of sand, shell and other detritus. In general, these worms have long tentacles which spread like spaghetti over the substrate. The tentacles collect algal and bacterial films from the sediments and tiny hairs (cilia) create currents that draw the food into a groove, along the tentacles to the mouth.

A number of polychaetes burrow through the sediments and ingest them, much like earthworms. The Capitellidae and Cirratulidae are both groups of polychaetes which feed in this manner. Capitellids are small, opportunistic, surface deposit-feeders. They live in semi-permanent mucous tubes and burrow rapidly through the sediments, feeding on algal and bacterial film, which they ingest through their proboscis. Their presence is often considered to be an indication that an area has been recently disturbed. This is because their life history traits of small body size, large eggs, continuous reproduction and short life span enable them to rapidly colonise new areas (Hsieh and Simon, 1991).

Syllidae, Guniadidae, and the Eulepethidae are all families which have species that are free living predators. These polychaetes are carnivores that roam across the sediment surface in search of food. There are even syllids which feed exclusively on hydroids, using their muscular pharynx to suck out the polyps. Free living, herbivorous polychaetes were represented by Nematonereis unicornis and a member of the Lumbrineridae.