Practice question

Trochophore is free-swimming ciliated larva considered basal for Spiralia, exhibiting apical sensory tuft, equatorial prototroch ciliary band anterior to mouth for swimming and feeding, metatroch, telotroch posterior, complete gut with anus and pair of protonephridia for excretion. In molluscan development, trochophore appears in polyplacophorans and some bivalves before transforming into veliger larva bearing foot, shell gland and mantle. Planula typifies cnidarians, nauplius crustaceans. Presence of trochophore in molluscs supports lophotrochozoan affiliation with annelids sharing spiral cleavage pattern, making it fundamental molluscan larval form despite direct development in cephalopods.