Morphological reinvestigation and characterization of the marine, sand-dwelling dinoflagellateAdenoides eludens(Dinophyceae)

The phototrophic, marine, sand-dwelling dinoflagellate Adenoides eludens (Herdman) Balech was isolated from intertidal sand of the North German Wadden Sea and subsequently cultured. For taxonomic purposes it was examined using light, scanning and transmission electron microscopy. Cells are slightly asymmetrical, oval to round, laterally flattened, 30.0 – 35.0 μm long and 23.0 – 28.0 μm deep. The theca is composed of 26 plates. According to our interpretation the plate formula is Po 4′ 6c 4s 5′′′ 5p 1′′′′ or alternatively it can be interpreted as Po 4′ 6c 5s 5′′′ 3p 2′′′′. All thecal plates are smooth with scattered pores. Dinoflagellate chloroplasts surrounded by three membranes display thylakoids grouped in stacks of three. Two stalked pyrenoids with a starch sheath are present. Spindle trichocysts were present and extruded through trichocyst pores. Additionally, intracellular gram-negative bacteria were found in the cytoplasm. Asexual reproduction is by desmoschisis. The position of Adenoides among the dinoflagellates is discussed, and we tentatively regard it as belonging to the gonyaulacoid lineage.