rhabdosome: a new type of organelle in the dinoflagellate Dinophysis

Most dinoflagellates contain trichocysts, ejectile organelles which are similar in structure to the spindle trichocysts of ciliates. These fusiform structures are enclosed by a single membrane and consist of a paracrystalline body and fibrous neck region. Typical trichocysts are absent in Dinophysis acuminata Claparede et lachmann, their place being taken by a different organelle, here called a rhabdosome, to the rod or thread-like organelles in the genus Phalacroma (presently incorporated into the genus Dinophysis ). The ultrastructure of these organelles is described here for the first time.