Swimming Manila Clam (Ruditapes philippinarum) larvae prior to settling out to begain a life in the substrate. These are 150-200 microns in diameter and the swimming organ (velum) and the foot are labeled. The width of the entire picture is slightly over 1mm.
PhylumMollusca - Molluscs e.g. snails, slugs, mussels, cockles & clams
Class Pelecypoda - Bivalves e.g. clams, cockles, mussels, oysters, and scallops