Distribution of molluscan remains in the sediment of the Chukchi Sea and its vicinity, the Arctic

The result of an analysis of mollusca remains collected from the Chukchi Sea,Beaufort Sea and Bering Sea in the First Chinese National Arctic Research Expedition,from July to September,1999 is presented.Seventeen species of mollusca have been identified,which belong to two classes:Bivalvia and Gastropoda.The compositions of the mollusca are very simple.According to the distribution pattern two groups may be distinguished among molluscan species.The Pan-Arctic and circumboreal group comprises Nuculana pernula,N.radiata,Nucula bellotii,Astarte montagui,Seripes groenlandicus,Macoma calcarea,M.moesta alaskana,Liocyma fluctuosa,Mya pseudoarenaria and Turritella polaris. Three species,Cyclocardia crebricos tata,Trichotrois coronata and Argobuccinum oregonense are components of the Pan-Arctic and Pacific boreal group.With regard to feeding habits,detritus feeders dominate.There are 7 species of detritus feeders,i.e.,Nuculana pernula,N.radiata,Nucula bellotii,Macoma calcarea,M.moesta alaskana,Macoma sp.and Trichotropis coronata.Detritus feeders are dominant with regard to the numbers of species as well as to the frequency of occurrence.Macoma calcarea is the most abundant species.