ABSTRACT
Three postmetamorphic developmental stages (viz. the juvenile, male and hermaphroditic stages) occur in Myzostomum cirriferum, a symbiote of the comatulid Antedon bifida. Juveniles are 100 to 500 um long without functional gonads, males measure from 500 to 700 um and have functional testes while hermaphroditics (i.e. adult worms) are 700 to 2,000 um long and possess both functional testes and an ovary. Juvenile and some male worms live attached to the ambulacral grooves of the pinnules of their comatulid host where they produce marked deformation of the lappets and podia, and behave as ectoparasites. Hermaphroditics and other males move freely on the host body wall; they do not produce any deformation of the host’ s body and behave as ectocommensals.
