Practice question

In phylum Ctenophora, statocyst functions as gravity-sensing balancing organ located aborally opposite mouth at apical pole. It contains lithocytes forming statolith mass resting upon balancers, four groups of ciliated cells connected to eight comb rows via nerve net. Displacement during tilt alters beating frequency of comb plates via transmission, restoring vertical orientation essential for feeding and locomotion. Structure resembles statocysts in cnidarian medusae but position aboral distinctive and statolith composition calcium carbonate. Platyhelminthes possess simple cerebral ocelli and occasional statocysts in turbellarians, rotifers rely on cerebral antenna and photoreceptors not statocysts, highlighting ctenophore equilibrium specialization for pelagic life.