Marine representatives of Phytomyxea (SAR: Rhizaria: Endomyxa), a peculiar class of obligate endobiotic parasites, are a greatly understudied ecological group of protists infecting many algal, diatom, and seagrass species. Very little is known about the actual diversity, ecology, and pathogenic potential of these organisms and their taxonomic treatment in many cases follows outdated morphotaxonomic concepts. Here we focused on resolving the phylogenetic relations of the phytomyxean parasites of the widespread seagrass genus Halophila. We report the first finding of Plasmodiophora halophilae, the parasite of ovate-leaf Halophila species, after more than 100 years since its original description in 1913. We provide additional information on its anatomy, morphology, distribution, and host range, together with a phylogenetic evidence that it is congeneric with the recently rediscovered species infecting the invasive seagrass Halophila stipulacea in the Mediterranean Sea. Despite the previously hypothesized affiliation of the latter to Tetramyxa, our phylogenetic analyses of the 18S rRNA gene place Tetramyxa parasitica (a parasite of brackish water phanerogams and the type species of the genus) in the freshwater/terrestrial phytomyxean order Plasmodiophorida and reveal that phytomyxids associated with Halophila spp. form a separate deep-branching clade within the class proposed here as Marinomyxa gen. nov. We further argue that M. marina infecting H. stipulacea is most likely a species-specific parasite and implies their comigration through the Suez Canal.

Phytomyxea (SAR: Rhizaria: Endomyxa) 的海洋代表是一类特殊的专性内生寄生虫，是一种未经充分研究的原生生物生态群，感染许多藻类、硅藻和海草物种。人们对这些生物的实际多样性、生态学和致病潜力知之甚少，而且在许多情况下，它们的分类处理遵循过时的形态分类学概念。在这里，我们重点解决了广泛分布的海草属Halophila的 phytomyxean 寄生虫的系统发育关系。我们报告了卵形叶嗜盐菌的寄生虫嗜盐嗜盐嗜盐菌的首次发现物种，自 1913 年最初描述以来已有 100 多年。我们提供了有关其解剖结构、形态、分布和寄主范围的更多信息，以及系统发育证据，表明它与最近重新发现的感染入侵海草Halophila stipulacea 的物种同源在地中海。尽管先前假设后者与四粘虫有关联，但我们对 18S rRNA 基因的系统发育分析将寄生四粘虫（一种微咸水显性寄生物和该属的模式种的寄生虫）置于淡水/陆地植物真菌目 Plasmodiophorida 中，并揭示了相关的 phytomyxa parasitica与嗜盐菌属 在此处作为Marinomyxa gen提出的类中形成一个单独的深分支进化枝。十一月 我们进一步认为，感染H. stipulacea 的M. marina很可能是一种特定物种的寄生虫，并暗示它们通过苏伊士运河迁徙。