A review of the Sentusidinium complex of dinoflagellate cysts

Wood, Stephanie E.L.; Riding, James B. ORCID:; Fensome, Robert A.; Williams, Graham L.. 2016 A review of the Sentusidinium complex of dinoflagellate cysts. Review of Palaeobotany and Palynology, 234. 61-93.

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The Jurassic to Neogene (Miocene) dinoflagellate cyst genus Sentusidinium has a relatively simple overall morphology. This genus, together with Batiacasphaera, Kallosphaeridium and Pentafidia, comprises the Sentusidinium complex. This is distinct from the superficially similar laterally asymmetrical and subspheroidal/lenticular Cyclonephelium complex. The genus Sentusidinium is an acavate, subcircular, proximate to proximochorate, sexiform gonyaulacacean genus with an apical archaeopyle and typically low relief ornamentation. Since the erection of Sentusidinium in 1978, three similar genera have been established, which we consider to be taxonomic junior synonyms of that genus: Barbatacysta, Escharisphaeridia and Pilosidinium. However, we deem the Early Cretaceous to Miocene genera Batiacasphaera, Kallosphaeridium and Pentafidia are deemed to be separate from Sentusidinium. We refine the definition of the Early Cretaceous to Miocene genus Batiacasphaera to circumscribe cysts with a reticulate to rugulate autophragm and an apical archaeopyle with a free operculum. By contrast, Kallosphaeridium has a ventrally attached apical archaeopyle with five plates that can be interpreted as type (4A1I)@ or type (5A)@; it also has a small operculum relative to the overall cyst diameter. The six accepted Kallosphaeridium species are confined to the Palaeogene. The Australian genus Pentafidia is unusual in appearing to only have five precingular plates; this comprises two species from the Jurassic–Cretaceous transition of Western Australia. Therefore, we emend Sentusidinium to restrict it to acavate, proximate or proximochorate dinoflagellate cysts with an autophragm devoid of, or covered with, highly variable, non-linear ornamentation and a type (tA) apical archaeopyle. Occasionally the elements of ornamentation may be connected, but rarely is a cingulum indicated, and the tabulation is never clearly evident. A kalyptra may be occasionally present. The operculum is free. Following a comprehensive literature review, we accept 17 species in Batiacasphaera. In Kallosphaeridium we accept six species confidently and consider six species to be problematical. We list 38 (34 accepted and four problematical) species of Sentusidinium. Kallosphaeridium? helbyi is here transferred to Cyclonephelium without question. The species Batiacasphaera angularis is occasionally tabulate and hence we transfer it, with question, to Meiourgonyaulax. The Sentusidinium complex is clearly polyphyletic, and all genera considered herein belong to the order Gonyaulacales. Batiacasphaera, Kallosphaeridium and Pentafidia cannot be confidently assigned to a family, whereas Sentusidinium belongs to the Gonyaulacaceae. The number of species within the complex has been reduced from 137 to 68; furthermore, all infraspecific taxa have been eliminated.

Item Type: Publication - Article
Digital Object Identifier (DOI):
ISSN: 00346667
Date made live: 10 Jan 2017 16:10 +0 (UTC)

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