COMPARATIVE PHYSIOLOGY OF SUSPENSION-FEEDING IN LIVING BRACHIOPODS AND BIVALVES - EVOLUTIONARY IMPLICATIONS

This paper presents scaling equations relating suspension-feeding rate s to body size for articulate brachiopods and bivalve molluscs, two cl asses which represent a significant component of the fossil record of marine benthic communities. Clearance (feeding) rates of five species of living articulate brachiopods and three species of epifaunal suspen sion-feeding bivalve molluscs collected from mid-latitude fjords of Ne wfoundland and New Zealand were measured in similar experimental condi tions. In comparisons within and between the two classes, we found tha t both plectolophous and spirolophous brachiopods had significantly lo wer feeding rates than mytilids, which are filibranchs, but that a sym patric primitive eulamellibranch veneroid bivalve had rates comparable to the brachiopods. Articulate brachiopods do not appear to feed effe ctively at the high algal concentrations which bivalves can exploit. T he data on comparative suspension-feeding rates support the hypothesis that past changes in diversity and distribution of bivalves and brach iopods may be related to an overall increase in energy flux and escala tion of metabolic rates during the Phanerozoic.