Odontochitina dilatata sp. nov. from the Campanian (Upper Cretaceous) of Poland: the importance of wall structure in the taxonomy of selected ceratiacean dinoflagellate cysts

摘要

Rich and well-preserved assemblages of organic-walled dinoflagellate cysts have been recovered from the upper Campanian of the Middle Vistula River section, central Poland. Among the ceratiacean dinocysts, the majority of the recovered specimens are attributed to the newly described Odontochitina dilatata sp. nov. Additional material comes from the Roztocze Hills (SE Poland). The most distinctive features of Odontochitina dilatata sp. nov. are: (i) widely divergent antapical and lateral horns, not connected by pericoel; and (ii) thick central body wall with a three-layered structure, consisting of endo-, meso-, and periphragm. The mesophragm, which is distinctly less homogeneous (spongy) than the other two layers, gives the central body wall a reticulate appearance. The three-layered wall structure is rarely recognised in dinoflagellate cysts, and this is its first record from the ceratiacean dinocysts. The genus Odontochitina is emended to emphasise its more complex wall structure and the importance of other features, such as the angle of divergence between the antapical and lateral horns and compression of the central body. Odontochitina dilatata sp. nov. shares its more complex wall structure with O. streelii and possibly also with Xenascus wetzelii, but differs in this aspect from O. costata, O. diducta, O. operculata and O. porifera. The distinction between the genera Odontochitina and Xenascus needs further discussion, since the only feature distinguishing them is a better development of the processes in the latter genus.