Polychaetes are largely marine annelid worms that are a major component of reef ecosystems. Most can be readily distinguished from opisthobranchs by their segmented bodies, leg-like parapodia and bristle-like setae. A few, however, have retractile tentacles lining the body that superficially resemble cerata or are broad and flattened resembling dorids. A close look at the undersides of these will reveal the segmentation and setae. They may be predators, scavengers or detritus feeders. Other, sedentary, tube-dwelling species have plume-like gills used in respiration and filter feeding. A few of the species most frequently mistaken for sea slugs:

Amblyosyllis sp. CP: Maui; April, 2007

Myrianida sp. CP: Maalaea Bay, Maui, Dec. 3. 2011

Iphione muricata CP: Maui; April, 2005

For more information see:   Polychaetes on the Sea Slug Forum Kwajalein polychaetes by Scott & Jeanette Johnson