Annelida- Worm

• Segmented schizocoelous worms with a complete digestive tract usually with regional specialization, a closed circulatory system, a well developed nervous system with a ventral nerve cord and segmental ganglia as well as a dorsal cerebrial ganglia, metanephridia, paired segmentally arranged epidermal setae bundles, a head composed of a presegmental prostomium and a peristomium, and usually with a trochophore larva.

sand worms, tube worms, clam worms, and others (Figure 2). With numerous setae (chaetae) on the trunk segments; most with well developed parapodia; prostomium and peristomium usually bear sensory organs (palps, tentacles, cirri) or extensive feeding and gas exchange tentacular structures; foregut often modified as eversible stomodeal pharynx (proboscis), sometimes armed with chitinous jaws; reproductive structures simple, often transient; without a clitellum; most are gonochoristic; development often indirect, with a free-swimming trochophore larva; mostly marine; burrowers, errant, tube- dwelling, interstitial, or planktonic; some live in brackish water, a few inhabit fresh water or are parasitic

• Prostmial appendages absent most burrowers or tube dwellers with a bulbous protrusable pharynx
  

The so-called lugworms have a rather thick, fleshy, heteronomous body divided into two or three distinguishable regions; pharynx unarmed but eversible and aids burrowing and feeding; live in intertidal and subtidal sands and muds in J-shaped burrows; direct deposit feeders

Body elongate and homonomous except that some mid-trunk segments are elongate, hence the common name of "bamboo worms"; burrow head downward and secrete a mucous sheath to which sand particles adhere, thereby forming a tube; proboscis unarmed by eversible and used in burrowing and selective deposit feeding.

with a pair of sensory palps on the prostomium

Long, cylindrical, tapered, homonomous body; enormous pharynx armed with four hooked jaws used in prey capture; large pharyngeal proboscis also used in burrowing; most are infaunal burrowers in soft substrata

Moderate to large polychaetes tending to homonomy; mostly errant predators with well developed parapodia; one pair of large curved pharyngeal jaws; some burrow, but most are epibenthic in protected habitats: among mussel communities, in holdfasts of algae, crevices, under rocks, et. (Internal anatomy)

External Anatomy

Body broad, oval or oblong, with less than 60 segments; with flattened, solelike ventral surface, and rounded dorsum covered with scales (elytra) overlaid by a thick felt- or hairlike layer, giving some the common name of "sea mouse"; slow moving, epibenthic or burrowers; most are omnivorous

• Sedentary species in tubes or burrows, groved palps used for deposit feeding.

Body fleshy, relatively large and distinctly heteronomous, divided into two or three functional regions with modified parapodia; chaetopterids live in more-or- less permanent U-shaped burrows lined with secretions from the worm, most are mucous-net filter feeders, eating plankton and detritus passed through the tube by water currents

Moderate-sized tube-dwelling polychaetes with fragile, fleshy bodies; heteronomous; body of two distinct regions; most lack eversible pharynx; most live in various types of permanent tubes (e.g., mud, sand, shell fragments); head bears numerous elongate feeding tentacles; most with 1-3 pairs of well developed branchiae on anterior trunk segments; feed on surface detritus

Tube-dwelling polychaetes commonly called "fan worms" or "feather-duster worms"; body heteronomous, divided into two regions similar to those of terebellids; pharynx unarmed and noneversible; peristomium bears a classy crown of branched, feathery tentacles that projects from the tube and functions in gas exchange and ciliary suspension feeding.

Heteronomous body divided into two regions; tube dwellers; anterior end bears a tentacular crown as in sabellids, plus a funnel-shaped operculum that can be pulled into the end of the calcareous tube when the worm withdraws; ciliary suspension feeders.