MORPHOLOGY AND ECOLOGY OF GLENO‐DINIUM ARMATUM LAVENDER (DINOPHYCEAE)

Faust, M. A. 1 and Kuosa, H. 21 Department of Systematics Biology, NMNH, Smithsonian Institution, Suitland, MD 20746; 2 Finnish Institute of marine Research, Helsinki, Finland FIN‐00931 Light and scanning electron microscopy were used to examine the morphology of Glenodinium armatum Levander, a small armored dinoflagellate from the Tvärminne Archipelago, Baltic Sea, Finland. This species is an important dinoflagellate in coastal rock pools. Cells are small, ovate, and dorso‐ventrally flattened. The cell surface is rugose with small round pores. The plate tabulation is: Po, x, 4', 2a, 7'', 6C, 5S, 5''', 2''''. Two intercalary plates are hexagonal and adjacent. Epitheca conical and hypotheca round and two antapical spines are present. The cingulum wide, slightly displaced and descending, and comprised of six cingular plates. Sulcal platelets are five and do not reach the antapex. Often in the hypotheca, a red horseshoe‐shaped stigma is present. Large nucleus situated posteriorly. Chloroplast golden brown and discoid. We suggest that G. armatum is a valid species with clear differences to Peridinium umbonatum Stein (syn. P. inconspicuum Lemmermann), but that it has not been always correctly identified. A new emended description is presented.