ABSTRACT Thalassiphora and other large ‘winged' dinoflagellate cysts common in Oligocene–Pliocene stratified epicontinental seas display morphological variation greater than the plasticity of extant taxa, thereby raising questions about causes. This variation has been attributed either to directed ontogeny in response to salinity or oxygen gradients or to evolutionary development in response to special environmental conditions. Some authors have grouped certain taxa that mark the closing phases of European Paratethyan basins into an intergradational plexus including species of Thalassiphora, Galeacysta, Nematosphaeropsis and cruciform Spiniferites. Spiniferites (previously Thalassiphora) balcanicus and Galeacysta etrusca were considered end members of this plexus, despite large differences in morphology. We re-evaluate interpretations of the plexus through comparison primarily with a new north-western Atlantic Eocene species Thalassiphora subreticulata and new Croatian material of Thalassiphora balcanica, and we comment on differences from other Thalassiphora species. The large Eocene species Thalassiphora subreticulata (up to 148µm maximum dimension) is camocavate, and has a coarsely reticulo-fibrous, irregularly perforate periphragm forming a shallow, bowl-shaped structure, as in Thalassiphora pelagica. Electron microscopy shows the perforations are crossed by fibrils in accord with a proposed ‘stretched net’ model of periphragm development. The smaller Late Miocene Paratethyan species Thalassiphora balcanica (maximum dimension to 115µm) is also camocavate, with a similar fibrous periphragm which encloses about half the ventral surface and has smooth-edged and open perforations. Scanning electron microscope images show this species lacks the branched spinous processes used to justify its transfer from Thalassiphora to Spiniferites by Sütő-Szentai. In both Thalassiphora species, morphological variations do not support either the benthic–planktonic stage ontogenetic model or the oxidation-state model previously proposed for Thalassiphora pelagica. Among 30 species currently assigned to Thalassiphora, no correlation was found between cyst size and age. However, the range of morphology in this genus points to the need for taxonomic re-assessment, which might help reveal evolutionary trends.

中文翻译：

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甲藻囊肿 Thalassiphora subreticulata n.sp., Thalassiphora balcanica：它们的分类、个体发育变异和进化

摘要 在渐新世-上新世分层的陆上海中常见的海海藻和其他大型“有翼”甲藻囊肿显示出的形态变异大于现存分类群的可塑性，从而引发了关于原因的问题。这种变化要么归因于响应盐度或氧梯度的定向个体发育，要么归因于响应特殊环境条件的进化发展。一些作者将某些标志着欧洲帕拉提亚盆地结束阶段的分类群归入一个交错丛，包括海洋藻属、Galeacysta、Nematosphaeropsis 和十字形 Spiniferites。Spiniferites（以前称为 Thalassiphora）balcanicus 和 Galeacysta etrusca 被认为是该丛的末端成员，尽管形态差异很大。我们主要通过与新的西北大西洋始新世物种 Thalassiphora subreticulata 和新的克罗地亚材料 Thalassiphora balcanica 进行比较来重新评估对神经丛的解释，并评论与其他 Thalassiphora 物种的差异。始新世大型种 Thalassiphora subreticulata（最大尺寸可达 148 微米）呈圆拱形，具有粗网状纤维状、不规则穿孔的周缘，形成浅的碗状结构，如深海海藻（Thalassiphora pelagica）。电子显微镜显示穿孔被原纤维穿过，符合所提出的牙周发育的“拉伸网”模型。较小的晚中新世 Paratethyan 物种 Thalassiphora balcanica（最大尺寸为 115 微米）也是圆孔状的，具有类似的纤维周缘，包围着大约一半的腹面，并具有边缘光滑和开放的穿孔。扫描电子显微镜图像显示，该物种缺乏 Sütő-Szentai 用来证明其从 Thalassiphora 转移到 Spiniferites 的分支棘突。在这两种海洋生物中，形态变异不支持底栖-浮游阶段个体发育模型或先前为海洋海洋生物提出的氧化态模型。在目前分配给 Thalassiphora 的 30 个物种中，未发现囊肿大小与年龄之间存在相关性。然而，该属的形态范围表明需要进行分类重新评估，这可能有助于揭示进化趋势。扫描电子显微镜图像显示，该物种缺乏 Sütő-Szentai 用来证明其从 Thalassiphora 转移到 Spiniferites 的分支棘突。在这两种海洋生物中，形态变异不支持底栖-浮游阶段个体发育模型或先前为海洋海洋生物提出的氧化态模型。在目前分配给 Thalassiphora 的 30 个物种中，未发现囊肿大小与年龄之间存在相关性。然而，该属的形态范围表明需要进行分类重新评估，这可能有助于揭示进化趋势。扫描电子显微镜图像显示，该物种缺乏 Sütő-Szentai 用来证明其从 Thalassiphora 转移到 Spiniferites 的分支棘突。在这两种海洋生物中，形态变异不支持底栖-浮游阶段个体发育模型或先前为海洋海洋生物提出的氧化态模型。在目前分配给 Thalassiphora 的 30 个物种中，未发现囊肿大小与年龄之间存在相关性。然而，该属的形态范围表明需要进行分类重新评估，这可能有助于揭示进化趋势。形态变化既不支持底栖浮游阶段个体发育模型，也不支持先前为海洋海藻提出的氧化态模型。在目前分配给 Thalassiphora 的 30 个物种中，未发现囊肿大小与年龄之间存在相关性。然而，该属的形态范围表明需要进行分类重新评估，这可能有助于揭示进化趋势。形态变化既不支持底栖浮游阶段个体发育模型，也不支持先前为海洋海藻提出的氧化态模型。在目前分配给 Thalassiphora 的 30 个物种中，未发现囊肿大小与年龄之间存在相关性。然而，该属的形态范围表明需要进行分类重新评估，这可能有助于揭示进化趋势。