Particle selection in suspension-feeding bivalves

Particle selection was studied in 10 species of suspension-feeding bivalves by comparing the proportion of algae in the pseudofaeces with that in the surrounding water. All species examined exhibited particle selection, but with different efficiencies. Spisula subtruncata was most efficient, followed, in decreasing order of efficiency, by Corbula gibba, Mytilus edulis (from Wadden Sea) , Acanthocardia echjnata, Aequipecten opercularis, Musculus niger, Crassostrea gigas, Mya arenaria, Cerastoderrna edule, Mytilus e d u l ~ s (from Qresund), and Arctjca ~s landica . Selection efficiency correlated with the size of the labial palps. Particles rejected as pseudofaeces were embedded in mucus, whereas ingested particles were always in free suspension in M. edulis. Apparently, then, different particles have different probabilities of being trapped in mucus, and thus rejected as pseudofaeces. The properties which determine this probability are unknown.