110 



NOAA Technical Report NMFS 140 



Only 4 (0.4% of total) of our samples yielded 

 specimens (10 individuals weighing a total of 

 4.60 g) whose mean density was <0.1/m 2 and 

 whose biomass was <0.01 g/m 2 (Table 5). 



Priapulids in the New England region were 

 found in the deep (1,420-2,035 m), cold (0- 

 3. 9°C), sand-silt and silt-clay bottoms of Georges 

 and Southern New England Slope waters, where 

 organic carbon levels range from 0.01 to 1.49%, 

 in very low abundance (Figs. 93-98). 



Mollusca 



The phylum Mollusca contributes significantly 

 to both measures of abundance (numerical 

 density and biomass) in the New England re- 

 gion as it does in the Middle Atlantic Bight 

 region (Wigley and Theroux, 1981). The mol- 

 luscan fauna comprises five classes: Poly- 

 placophora. Gastropoda, Bivalvia, Scaphopoda, 

 and Cephalopoda. Each of these classes will be 

 discussed separatelv below. For the sake of con- 

 tinuity in the phylogenetic ordering of figures, 

 those figures dealing with phvlum Mollusca (Figs. 

 99-104, inclusive) are included here, but a de- 

 tailed discussion of the phylum as a whole will 

 be presented in the section "Dominant Com- 

 ponents of the Macrobenthos" below. 



Polyplacophora — This class of mollusks is also 

 called chitons, which are bilaterally symmetri- 

 cal, have eight overlapping dorsal plates, and a 

 broad, flat, ventral foot. Thev accounted for 

 less than 1% of the biomass and number of 

 animals of the total benthic invertebrate fauna 

 (Table 3). 



Specimens ranged in size from 4 mm to 2 cm 

 and exhibited considerable variation in color. 

 They were commonly chalky white or various 

 shades of light gray; a small proportion were 

 light brown. A few had a dark, nearly black 

 coating over their plates that contrasted sharply 

 with the underlying white or light gray. 



Chitons were relatively common in the coastal 

 areas, on relatively shallow offshore banks, on 

 coarse bottom sediments, and where the water 

 temperature range was moderately broad. 



Polyplacophorans occurred in 84 samples 

 (8% of total). Their density averaged 1.5/nr. 

 and biomass averaged 0.14 g/m- (Table 5). 



Geographic Distribution 



Polyplacophorans, although rather sparse, oc- 

 curred in small to moderately large geographi- 



5 

 O 



is 



2 <f> 



O O NUMBER - 



WEIGHT 



\ 



A 



oj—rir 



I \ ' 



25 50 100 200 500 1000 2000 4O00 

 WATER DEPTH IN METERS 



Figure 89 

 Density and biomass of Echiura in relation to water depth. 



