Restudy of the holotype of Operculodinium centrocarpum (Deflandre & Cookson) wall (Dinophyceae) from the Miocene of Australia, and the taxonomy of related species

Operculodinium centrocarpum (Deflandre & Cookson) Wall 1967 is one of the most commonly reported dinoflagellate cysts (dinocysts) in samples from Tertiary and Quaternary deposits. However, at least two distinct dinocyst morphologies are assigned to this species in the literature at the present time. In addition, two separate species have been erected for one of these distinct morphologies. In order to define criteria with which to differentiate these morphologies, holotype and topotype material of O. centrocarpum (Deflandre & Cookson) Wall 1967 and O. echigoense Matsuoka 1983 were restudied and compared with dinocysts of Protoceratium reticulation (Claparéde & Lachmann) Bütschli 1885. Re‐investigation of the holotype and topotype specimens of O. centrocarpum (Deflandre & Cookson) Wall 1967 (=Hystrichosphaeridium centrocarpum Deflandre & Cookson 1955) and O. echigoense Matsuoka 1983 demonstrated that O. echigoense Matsuoka 1983 is a junior synonym of the former. This restudy also confirmed that O. centrocarpum (Deflandre & Cookson) Wall 1967 (= H. centrocarpum Deflandre & Cookson 1955) is morphologically distinct from the Quaternary dinocysts that are widely attributed to this species in the literature. [These Quaternary forms are referred to in this paper as O. centrocarpum (Deflandre & Cookson) sensu Wall 1967.] Viable cysts that are morphologically identical to the Quaternary forms [i.e., O. centrocarpum (Deflandre & Cookson) sensu Wall 1967] have been incubated to produce the motile dinoflagellate P. reticulatum (Claparéde & Lachmann) Bütschli 1885. We propose that, 1) the latter name should be applied only to large, morphologically distinct dinocysts comparable to those originally described from the Miocene of Australia, and 2) the distinctive Quaternary forms [i.e., O. centrocarpum (Deflandre & Cookson) sensu Wall 1967] should be referred to as the cysts of Protoceratium reticulatum (Claparéde & Lachmann) Bütschli 1885. © 1997 Taylor & Francis Group, LLC.