Limits and constraints: A comment on premises and methods in recent studies of particle capture mechanisms in bivalves

The moving seascape of research into bivalve suspensionfeeding mechanisms presents challenges which suffice to redirect many curious biologists toward less choppy waters. The anatomical complexity of the various pallial organs alone leave many potential workers bewildered. The range of techniques employed is also rather spectacular, from clearance studies to endoscopy, flow cytometry, confocal microscopy, new histochemical techniques, and ciliary mapping, each with different constraints and generating different types of information. The scales involved simultaneously span the molecular and the organismic. And then there is the unfortunate tendency of the handful of workers in this field to form rigid schools of thought, periodically circling the wagons and shooting in all directions (e.g., Jørgensen 1996). The paper by my colleagues Ward et al. (1998a) entitled ‘‘A new explanation of particle capture in suspension-feeding bivalve molluscs,’’ derives its ‘‘new explanation’’ of particle capture exclusively from video endoscopic observations. Many of the basic ideas were presented in Ward (1996), although the present paper concentrates somewhat more on the roles of the laterofrontal cilia/cirri. I would like to point out some questionable preliminary suppositions and generalizations, limitations of the methodology which limit depth of analysis, and indicate the most useful areas of contribution of endoscopy.