TAXONOMY AND MORPHOLOGY OF DINOFLAGELLATE CYST GENUS HOROLOGINELLA COOKSON AND EISENACK 1962
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Abstract:
Following the original definition the genus Horologinella includes the microfossils of small size and specifichour-glass shape. Various types assigned to this genus can be divided into two groups of sufficiently different morphology:tabulated and nontabulated forms, that confirms rather confusion situation withing the taxonomy of genus Horologinella.Tabulated Horologinella forms have been extremely rare observed in palynological assemblages and a little information isavailable concerning the morphology, stratigraphic range and palaeoenvironmental characteristic of these palynomorphs. Agood preservation of numerous specimens of species H. anabarensis Pestchevitskaya 2001, described from Lower Cretaceoussediments of Anabar Bay section (North of Middle Siberia), allows to investigate the morphology of tabulated Horologinellaforms in details. The paratabulation pattern of precingular, postcingular and apical series as well as configuration of first apicalhomologue and parasulcal structure suggest that tabulated forms of Horologinella have close affinities to gonyaulacaleandinoflagellate cysts, especially to members of suborder Rhaetogonyaulacaceae. Paleontological and palynological data evi-dence that H. anabarensis is associated with shallow marine environments favorable for the development of rather richmicrophytoplankton assemblage.
