Emendation of the genera <i>Selenopemphix</i> and <i>Multispinula</i> (Peridiniales, Dinophyceae), with the description of <i>Multispinula varispinosa</i> sp. nov. and <i>Multispinula robusta</i> sp. nov.

Abstract. The taxonomy of the dinoflagellate cyst-based genera Selenopemphix and Multispinula has long needed revision. This is accomplished here by a multiproxy approach combining incubation experiments and morphological and molecular (partial LSU rDNA) analyses focusing on the respective type species Selenopemphix nephroides and Multispinula quanta. Additionally, cyst wall composition is analysed via attenuated total reflection Fourier transform infrared microspectroscopy (ATR µ-FTIR) to assess the diversity and preservation of cyst wall biomacromolecules. New molecular phylogenetic analyses demonstrate that the two species are polyphyletic, supporting the distinction of two cyst-based genera. Morphological features further support this distinction and justify emended diagnoses for both genera. The genus Selenopemphix is emended to include only cysts with an offset archeopyle and ornamentation restricted to the paracingular margins, while the genus Multispinula is emended to include cysts with a mid-dorsal archeopyle and paratabulation outlined by parasutural ridges and spiny processes present in the precingular and postcingular regions. Selenopemphix quanta is transferred back to its initial name Multispinula quanta. Furthermore, two new species, Multispinula robusta sp. nov. and Multispinula varispinula sp. nov., are described as cyst stages of Protoperidinium conicum and Protoperidinium parvivariplatum sp. nov. In addition, our results confirm the equivalence between S. nephroides and Protoperidinium subinerme. Cysts of modern Multispinula and Oligocene to modern Selenopemphix nephroides exhibit a proteinaceous and pigmented (melanised) wall composition, common for protoperidinioids. However, Multispinula cysts are chemically distinct from Selenopemphix cysts in being relatively less melanised and more enriched in proteins. High protein abundances in dinocyst walls are evaluated to negatively affect preservation potential. This study stabilises the taxonomy of the cyst genera Multispinula and Selenopemphix and highlights the value of integrating morphological, molecular, and cyst wall chemical analyses to resolve issues in dinoflagellate cyst taxonomy.