Annulated (segmented) worms
The body of an annulated worm consists of a definitive, linear series of segments as illustrated in the photograph of a marine earthworm, p. 131 (Lumbrineridae). This external segmentation is reflected internally by the compartmentalization of various organ systems. Each segmented worm possesses a body-length digestive tract with an anterior mouth and a posterior anus. Although virtually everyone’s introduction to the segmented worms is via an encounter with the familiar backyard earthworm (an oligochaete) or the dreaded fresh-water leech, it is the polychaetes—“worms with many bristles”—that flourish in the marine environment. They are the “Cadillacs” of the annelid world! The diversity of segmented worms in the world has been estimated at more than 22,000 species, and at least 9,000 of these are polychaetes, the vast majority of which are marine.
Historically and for various reasons, annelids have received minimal attention in the popular press. Though there are many species of marine oligochaetes, it is a select group of leeches and polychaetes that are featured below. Additional introductory material for each family is included.