The phylogenetic significance of some anatomical features of bivalve veliger larvae

Abstract Various larval types are present within the Bivalvia. The primitive protobranchs have barrel-shaped test or pericalymma larvae, some freshwater bivalves have parasitic larvae such as the glochidium or lasidium, but the most common larval development pattern involves a shelled ciliated stage, the veliger. In some cases, the veliger is lecithotrophic and may, where a free-swimming stage is short-lived or absent, be highly modified or reduced in comparison to the more characteristic planktotrophic form (Chanley, 1969).