Ultrastructure of two toxic marine dinoflagellates, Prorocentrum lima and Prorocentrum maculosum

Abstract

Two benthic and epiphytic toxin-producing marine dinoflagellates, Prorocentrum lima (Ehr.) Dodge and Prorocentrum maculosum Faust, were examined using light microscopy, scanning electron microscopy and transmission electron microscopy. P. lima is oblong in face view and is characterized by numerous marginal pores. P. maculosum is broadly ovate and possesses a distinct flange around the cell edge. The electron density of chromosomes relative to nucleoplasm in the two species differs; P. lima chromosomes are consistently more electron dense than P. maculosum. In both species, two flagella emerge through a single flagellarcanal. Flask-shaped membrane-bounded organelles termed mucocysts are present in both species as well as two large spherical pyrenoids covered by thick starch sheaths. PAS (Periodic acid/Schiff) bodies and coated vesicles occur in the cytoplasm together with numerous single membrane-bounded vesicles surrounded by endoplasmic reticulum and ribosomes. No endocellular bacteria were observed in any of the cells examined.