WIGLEY and STINTON: REMAINS FROM MARINE SEDIMENTS 



Table 5. — Species and density, by stations, of pelecypods 

 that occurred at only one station each. 



Species 



Station 



Specimens 



Abra tongicallis 

 Aequipectfn gtyptus 

 Anadara ovalis 

 Axinopsis orbiculata 

 Bathyarca anomala 

 Crenetla ptctinula 

 Cuspidaria striata 

 Cyrtodaria siligua 

 Liocyma jluctuosa 

 Macoma balthica 

 Modiolus dftnissus 

 Myonrra limatula 

 Mytilus edulis 

 Nucula dflphinodonta 

 Nuculana tenuisulcata 

 Panomya arctica 

 Ptriploma afjinis 

 Siliqua costata 

 Solimya velum 

 Tellina agilis 

 Thracia conradi 

 Thracia myopsis 



2) 

 10 

 16 



8 

 56 

 33 



8 

 30 

 30 



6 

 46 



3 



1 



11 

 38 

 25 



4 

 17 



4 

 29 

 13 



5 



Nolrrfi 



10 



10 



10 

 50 

 80 

 20 

 20 

 20 



10 



10 



10 



10 



10 



10 



10 



10 

 20 

 20 



10 



10 

 40 

 20 



41' 



40'- -'0° T 



200 ipq^^ii: 

 500 



ipOO METERS 



t -. _n ^ '■:>.»-.-- '^ 



EZI3 0-1,000 



PELECYPODA 

 NUMBER PER M* 



F=^ lOOO-SpOO T771 OVER jpoo 



T 1 r 



T\' 



ro* 



Figure 8. — Density distribution of pelecypod shells, all 

 species combined. 



Pelecypods were sparse (less than 50/m^) or 

 absent at 8 stations, common (50 to 1,000/m-) 

 at 32 stations, abundant (1,000 to 3,000/m-) at 

 16 stations, and very abundant (more than 

 3,000/m-) at 6 stations. 



Pelecypod shells were present at all depths 

 sampled (Table 6). Densities were lowest (30 

 to 40/m-) at both the shallowest and deepest 

 stations; moderate (100 to 1,100 'm-) between 

 30 and 89 m and between 200 and 249 m; high 

 (greater than l,100/m2) between 125 and 199 m; 

 and highest (more than 2,000/m-) from 90 to 

 124 m. 



Table 6. — Density distribution of pelecypod shells, all 

 species combined, in relation to water depth. 



Water 

 depth 

 class 



Samples 

 collected 



Samples 



containing 



pelecypod 



shells 



Mean 

 number 



of 

 shells 



Mettrs 



20-29 



30-39 



40-49 



50-59 



60-69 



70-79 



&0-89 



90-99 



100-124 



125-149 



150-174 



175-199 



200-249 



250-567 



Number 

 1 



6 



7 

 8 

 5 

 9 

 1 



7 

 4 

 4 

 I 



5 

 2 

 2 



Percent 

 100 

 100 

 86 

 63 

 100 

 100 

 1O0 

 100 

 100 

 100 

 100 

 100 

 100 

 100 



No/m^ 



30 



140 



440 



320 



670 



1,030 



620 



2,250 



3,080 



1,110 



1,460 



1,970 



690 



40 



Relations of Density to Sediments 



Pelecypods were generally more abundant in 

 moderately fine-grained sediments than in either 

 coarse or very fine types. Silty sand, sandy silt, 

 and sand-silt-clay were most commonly associ- 

 ated with high density. Average shell density 

 in these three substrate types ranged from 1,800 

 to 3,300/m-. Shells were absent or sparse in 

 gravel-sand substrates (average density 80 /m=) 

 and silts (average density 40/m-), and moder- 

 ately low (average 650/m-) in sand. 



Distribution and Density by Species 



Geographic distributions of the 35 more com- 

 mon pelecypod species are illustrated in Figure 

 9. These charts are based on information listed 

 in Table 4. No two species had identical distri- 

 butions, but the distribution of a number of spe- 

 cies in east-west bands across the study area sug- 

 gests correlations with hydrographic features 

 or bottom sediments, or both. 



11 



