Meringosphaera is an enigmatic marine protist without clear phylogenetic affiliation, but it has long been suggested to be a chrysophyte-related autotroph. Microscopy-based reports indicate that it has a worldwide distribution, but no sequence data exist so far. We obtained the first 18S rDNA sequence for M. mediterranea (identified using light and electron microscopy) from the west coast of Sweden. Observations of living cells revealed granulated axopodia and up to 6 globular photosynthesizing bodies about 2 μm in diameter, the nature of which requires further investigation. The ultrastructure of barbed undulating spine scales and patternless plate scales with a central thickening is in agreement with previous reports. Molecular phylogenetic analysis placed M. mediterranea inside the NC5 environmental clade of Centroplasthelida (Haptista) along with additional environmental sequences, together closely related to Choanocystidae. This placement is supported by similar scales in Meringosphaera and Choanocystidae. We searched the Tara Oceans 18S V9 metabarcoding dataset, which revealed four OTUs with 94.8%–98.2% similarity, with oceanic distribution similar to that based on morphological observations. The current taxonomic position and species composition of the genus are discussed. The planktonic lifestyle of M. mediterranea contradicts the view of some authors that centrohelids enter the plankton only temporarily.

中文翻译：

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长期孤儿原生生物 Meringosphaera mediterranea Lohmann，1902 [1903]

Meringosphaera是一种神秘的海洋原生生物，没有明确的系统发育隶属关系，但长期以来一直被认为是与金藻相关的自养生物。基于显微镜的报告表明它在世界范围内分布，但到目前为止还没有序列数据。我们获得了M的第一个 18S rDNA 序列。 来自瑞典西海岸的地中海（使用光学和电子显微镜鉴定）。对活细胞的观察揭示了颗粒状的轴足和多达 6 个直径约 2 μm 的球状光合作用体，其性质需要进一步研究。有刺波状棘鳞和中央增厚的无花纹板鳞的超微结构与之前的报道一致。分子系统发育分析米。 Centroplasthelida (Haptista) 的 NC5 环境进化枝内的地中海以及其他环境序列，与 Choanocystidae 密切相关。这种位置得到了Meringosphaera和 Choanocystidae 类似鳞片的支持。我们搜索了 Tara Oceans 18S V9 元条形码数据集，发现 4 个 OTU，相似度为 94.8%–98.2%，海洋分布与基于形态学观察的相似。讨论了该属目前的分类地位和物种组成。M的浮游生活方式。 mediterranea与一些作者的观点相矛盾，即中心天体只是暂时进入浮游生物。