Polychaete Worms [Annelida]

Most of the worms recorded by scientists in Great Bay Estuary are annelids, or segmented worms. The word annelid is derived from the Greek word annulatus, meaning ringed. Rings separate these worms into segments, which bear repeated sets of muscles, nerves, blood vessels and excretory organs. One benefit of this arrangement is more flexible locomotion. Each segment moves independently, extending when the muscle encircling it contracts, and bunching up when the longitudinal muscle inside it contracts.

Unidentified polychaete worm species

In Great Bay Estuary, these are primarily polychaetes ("many bristles”), a class of annelids with flap-like appendages on the sides of their segments. These flaps, or parapodia, are usually embedded with bristle-like chaetae. Used in locomotion, breathing and feeding, the parapodia of various species range from pimple-like sensory projections to paddle-like flaps. Why the variation? Basically, varied body parts reflect varied worm lifestyles. There are two general polychaete groups.

Errant polychaetes tend to be on the move rather than staying put in their tubes or burrows. The flat 15-scale worm uses its parapodia for crawling. Paddle worms and some clam worms have the paddle-shaped parapodia, which make them good swimmers. Creeping Syllis worms have a slender tactile projection in each of their parapodia.

Most errant polychaetes are also carnivores, and so have larger, more elaborate proboscises. The proboscis is the part of the digestive tract that many worms turn inside out through their mouths to consume their prey. Some are outfitted with jaws, hooks, minute teeth, and even fangs. Clam worms, paddle worms, red-lined worms and 15-scaled worms use their proboscises to prey on invertebrates that, depending on the species, may include small clams, worms, crabs, or barnacles. Many of these same worms also scavenge plant remains.

Sedentary polychaetes tend to stay in their burrows or tubes in the sediments, so they don’t need well-developed parapodia or elaborate proboscides. The bamboo worm has just little folds for parapodia on its narrow, cylindrical body segments. Living with its head down in the sediments feeding on tiny particles, this worm doesn’t depend on agile movement.

But sedentary polychaetes do have enhanced appendages for stationery feeding and respiration. Spaghetti-mouth worms and some mud worm have long tentacles on their heads, called palps, which sweep food particles from surface sediments. Similarly, fringed worms are topped with bunches of long thread-like gills, which reach out of surface sediments to breath. Fan worms extend tentacles with a featherduster structure into the water column to breathe and strain out food particles. Mud worms use their long, often coiled palps to collect food. Several of mud worm species also use gills projecting from their segments to breathe.

Worm Roundup
To put the Segmented Worms (phylum Annelida) of Great Bay Estuary into context, it helps to consider the general physical characteristics of the other five divisions of worms.

The flat worms (phylum Platyhelminthes) have very flat bodies with no segments or appendages. Many coastal species are an inch or less in length. Kenneth Gosner likened their swim above substrates to “tiny flying carpets.”

Ribbon worms (phylum Nemertea) are long, flat and without segments. Three-foot length is average.

Peanut worms (phylum Sipunculida) have two sections. The introvert is the narrow, probing section of the anterior (front). A mouth and sometimes tentacles are on the end. The introvert is pulled into the posterior (back) section called the trunk.

Acorn worms (phylum Hemichordata) have three distinct sections: a burrowing proboscis, a small collar containing the mouth, and a trunk with gills.

Arrow worms (phylum Chaetognatha) are plankton, less than an inch long. Their elongate bodies, with head, fins, and tail, dart around in the upper water column.

Copyright © 2006 Barbara Driscoll.