adult ctenophore Pleurobrachia species maintain cydippid forms as adults, but the others become radically different: M. leidyi greatly reduce their tentacles and form large oral lobes; B. ovata lack tentacles and form large oral lips that they use to engulf or nip at other ctenophores; and platyctenes become compressed in the oral-aboral direction and adopt a sessile or creeping lifestyle, crawling around the substratum rather than locomoting by beating their ctene rows. cydippid larva ctenophore adult stage multicellular organism adult organism