Abstract

Among dinoflagellates, extant cladopyxidaceans may provide a missing link to better understand the first evolutionary transformations from ancestral configurations toward the more abundant and more derived patterns in Gonyaulacales and Peridiniales. A restudy of the extant, motile-defined Micracanthodinium setiferum using plankton samples from the Indian and Atlantic oceans and the Mediterranean Sea demonstrates that the correct plate formula is Po, Pt, X, 3′ + *4′, 4a, 7′′, 7C, 4S, ?6′′′, 0p, 2′′′′. A ventral pore is found between 1′, 3′ and *4′. A restudy of the extinct, fossil-defined Cladopyxidium saeptum from the upper Paleocene of Delaware (USA), demonstrated the presence of an identical tabulation. A ventral pore (= porichnion) was positioned between *1′ and 7′′. Cladopyxidium is morphologically closer to Micracanthodinium than to Cladopyxis. Since Cladopyxidium has been extinct since the middle Eocene, it is unlikely that Micracanthodinium and Cladopyxidium have a direct biological link; the close morphological similarity between them does, however, suggest an important phylogenetic relationship between them in the evolution of cladopyxidaceans.

摘要

在甲藻中，现存的枝栉目动物可能提供了一个缺失的环节，以更好地理解从祖先配置到 Gonyaulacales 和 Peridiniales 中更丰富和更衍生的模式的第一次进化转变。使用来自印度洋和大西洋以及地中海的浮游生物样本对现存的、运动性定义的Micracanthodinium setiferum进行的重新研究表明，正确的板块公式是 Po, Pt, X, 3' + *4', 4a, 7'',图7C，4S，Δ6'''，0p，2''''。在 1'、3' 和 *4' 之间发现了一个腹孔。对来自特拉华州（美国）上古新世的已灭绝的、化石定义的Cladopyxidium saeptum的重新研究表明存在相同的表格。腹孔（= porichnion）位于*1'和7''之间。Cladopyxidium在形态上更接近Micracanthodinium而不是Cladopyxis。由于从始新世中期开始，枝条藻就已经灭绝，因此小角藻和枝条藻不太可能有直接的生物学联系；然而，它们之间密切的形态相似性确实表明它们之间在枝状角类动物的进化中存在重要的系统发育关系。