Pelagic larvae of marine bottom invertebrates are able to perform different types of active vertical movements in marine nearshore and estuarine waters. The speed of these active movements is in the order of magnitude of common representatives of marine micro-and mezo-holozooplankton performing daily vertical migrations, and only slightly less than that of holozooplankton. Only a few morphological types of larvae, characterized by weak ciliary movement apparatus (amphiblastulae of sponges, ophioplutei) have a speed of movement less than I cm 9 min-L All other types of larvae, which possess strong ciliary movement apparatus or swimming appendages, are characterized by quick active movement from more than I to 60 cm 9 min -i in lamellibranch larvae, and up to I17 cm โข min -i in decapod larvae. Because of their ability to produce sufficient speed of active movement, pelagic larvae of bottom invertebrates are able to control their vertical distribution in marine nearshore and estuarine waters in all neritic regions, including those with very strong tidal currents, except where local water stratification inhibits their active vertical movement.