Phyllodocida is an order of polychaete worms which contains an estimated 3500+ species. Adults range in size from several millimeters to more than a meter. Morphological studies cite strong support for a monophyletic grouping of the Phyllodocida, based on several characters (anterior enlarged cirri; an axial muscular proboscis (eversible pharynx); ventral position of sensory palps; compound chaetae with a single ligament; lack of dorsolateral folds; see Rouse and Fauchald, 1997).
The phyllodocida span a range of habitats. While most are marine, some live in brackish waters, and members of the family Nereididae can be found in freshwater and even terrestrial environments. The Phyllodocida make up a large portion of what have been considered the “errant” polychaetes – active burrowing and swimming worms. Most of the marine members of the Phyllodocida are free-living burrowers; some groups spend their adult lives in the water column (these pelagic species are usually transparent). A very few are sessile and live in tubes (Pleijel and Rouse 2004).
Several molecular studies carried out since then have questioned the monophyly of the Phyllodocida, although it is recognized that none of these studies have very complete taxon sampling (Rousset et al. 2006, and references within). It has been difficult to root the polychaete tree, and it has been suggested that the root of the polychaetes lies within the Phyllodocida, rendering this group paraphyletic (Rouse and Pleijel, 2001)
Worms in the order Phyllodocida generally are predators or scavengers. They have a eversible proboscis, which in many is bestowed with large jaws (many species can deliver a powerful bite to humans), a large head with well developed eyes and sensory structures. The front segments have sensory appendages called cirri, while the segments further back have broad appendages called parapodia for crawling or swimming, and which support bunches of chaetae in species-specific patterns.
Some of the rag worms (Neries and close relatives) and blood worms (Glycera) are harvested commercially for fish bait, and are among the most widely known of the phyllodocida.
