228 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 22 



COMMUNITIES 



The description of communities has been a common endeavor in 

 shallow marine waters but only to a small extent in deeper waters 

 (see Thorson, 1957, and Bruun, 1957). Thorson has reviewed the 

 community naming problem and set a list of standards which we are 

 following in our shallow shelf work. According to Thorson, com- 

 munities should be designated by names of common species dominating 

 the samples by their frequency, replicativeness and standing crop. Thus, 

 a single large echiuroid in a sample, though the largest part of the 

 crop, is not a useful designator for a community, whereas some nu- 

 merous organism of secondary weight importance is more useful, since 

 it occurs repeatedly in the samples. On this basis, we have assembled 

 the following list of common and characteristic species of the basins. 



The common recurrence of Phyllochaetopterus Umicolus, Protis 

 pacifica and dead shells of Cyclopecten zephyrus (living members of 

 which probably are able to escape the grab), with their dominant 

 aggregate crops, indicates that the subsill San Pedro and Santa Monica 

 Basins can be designated as communities by those appellations. 



The remaining Basins, except Santa Barbara and Velero, have two 

 species of common recurrence and major crop, Aricidea uschakovi and 

 Tharyx tesselata, both polychaetes, by which we believe this bathyal 

 basin community can be named. However, Tharyx tesselata is of minor 

 importance in several basins, as seen below; but the frequency of sam- 

 pling is low in most of those. Several Basins have differing facies 

 and other major components which differentiate them from their fellow 

 basins. Although the above two polychaetes are indicators in San Nicolas 

 Basin, two other species, an unknown sipunculid and the clam Solemya 

 fjohnsoni, dominate. The sipunculid is quite numerous and the con- 

 spicuous part of each sample, while the Solemya, occurring nearly 

 universally but only in ones or twos per sample, constitutes the principle 

 crop. Thus, San Nicolas Basin might be called a subcommunity or 

 facies dominated by these two species. Tanner Basin supports the 

 Solemya as well, but not the sipunculids. West Cortes, San Clemente 

 and East Cortes Basins have a characteristic polychaete species as sub- 

 dominant, Ceratocephala loveni pacifica, and might be classified as a 

 facies of the Aricidea-Tharyx community. San Clemente Basin has in 

 addition a characteristic sea-whip Dtsttchoptilum verrillii which, like 

 the Sole?nya of San Nicolas, occurs in ones or twos but in submarine 



