180 



U.S. NATIONAL MUSEUM BULLETIN 227 



naths, followed by several rows of smaller ones which diminish in 

 size posteriorly. 



Color, in life: iridescent greenish brown, rich golden brown, reddish 

 brown, light brown, olive green, yellowish, violet; color, preserved: 

 uniformly purplish, reddish, some with dorsal chri and ligules dark 

 distally. 



At maturity, sexually dimorphic heteronereids are formed. The 

 eyes are greatly enlarged. The body is divided into 2 regions, 

 anterior region with the usual type of setae and posterior region 

 with the usual type of setae replaced by swimming setae, segments 

 compressed and flattened anteroposteriorly, with extra development 

 of lamellar plates on neuropodia and bases of dorsal and ventral cirri. 



Table 3 below shows how the sexually dimorphic males and females 

 differ. 



Table 3. — Differences between sexually dimorphic males and females in N. (Nereis) 



pelagica 



Biology. — Found intertidally on rocky shores, under rocks, in 

 crevices, among mussels (Mytilus) and sponges (as Halichondria), 

 on algae, including holdfasts of Laminaria, under incrusting algae 

 (as Lithothamnion) on rocks. Confined mostly to the lower half of 

 the intertidal zone. Found on pilings, floats, among tunicates, 

 sponges, hydroids, etc. May form membranous tubes attached to 

 algae. Found on floating kelp and sometimes washed upon the beach 

 after storms along with the kelp (as Laminaria, Fucus). Very numer- 

 ous in the oceanographic fouling studies in the New England region. 

 Dredged on bottoms of sand, gravel, stones, rocks, rarely in mud, 

 among shells, bark, algae (including "weed" from Lagoon Pond), 

 sponge masses, bryozoan nodules, compound tunicates (as sandy 

 Amaroecium pellucidum) , corals, and worm tubes. The species is 



