A comparison of traditional, cluster and Z�rich-Montpellier analyses of infaunal pelecypod associations from two adjacent sediment beds

A Zurich-Montpellier analysis provided more detailed information about pelecypod associations in two sediment beds than either a traditional subjective approach or a cluster analysis based on Jaccard's coefficient. The Zurich-Montpellier test separated till and sand pelecypod associations, and indicated distinguishing species and atypical samples. Species distinguishing the till association were Cardita ventricosa, Yoldia myalis, Semele rubropicta, Venerupis kennerlyi, Clinocardium nuttallii, Nuculana minuta and Macoma incongrua. Species distinguishing the sand were Macoma elimata, Compsomyax subdiaphana, Yoldia ensifera, Macoma calcarea, M. lipara, M. brota, Yoldia limatula and Macoma alaskana. Two samples contained species from both associations plus some species rare elsewhere. Combined R-and Q-type grouping procedures, of which the Zurich-Montpellier approach is an example, are useful in evaluating benthic faunal similarities, but the suitability of various forms of the procedure needs further study.