Species of the genus Ellipsomyxa Køie, 2003, parasitize mostly marine and brackish fish around the world. In the present study, we describe two novel species of Ellipsomyxa: Ellipsomyxa plagioscioni n. sp. parasitizing the gall bladder of Plagioscion squamosissimus (Sciaenidae), a freshwater fish but commonly found in brackish water in the Amazonian estuarine environment; and Ellipsomyxa paraensis n. sp. infecting Cichla monoculus (Cichlidae), a strictly freshwater fish. The host specimens were caught from the Amazon and Tapajós rivers, in the municipal region of Santarém, in the State of Pará, Brazil. The study was performed using a combination of morphological, biological, and SSU rDNA-based phylogeny, which suggested that marine transgressions of the Miocene epoch, in the central region of South America, were a pathway for the adaptation and radiation of these cnidarian parasites in the freshwater environment. Both disporic plasmodia and mature myxospores were found floating freely in the bile. Mature myxospores from both species were ellipsoidal in the valvular and sutural views, with thin smooth valves elongated in the direction perpendicular to the plane of the transverse sutural line. Ellipsomyxa plagioscioni n. sp. myxospores measured 11.1 (10.2–12.8) µm in length and 6.6 (5.6–7.6) µm in width. Two pyriform polar capsules discharging on opposite sides, some distance from both the sutural line and the spore ends, measured 3.8 (3.2–4.4) µm in length and 2.8 (2.3–3.3) µm in width, with 5–6 coil polar tubules. Ellipsomyxa paraensis n. sp. myxospores measured 11.5 (10.5–12.4) µm in length and 7.5 (6.6–8.6) µm in width. Two pyriform polar capsules which discharged on opposite sides some distance from both the sutural line and spore ends, measured 3.2 (2.1–3.9) µm in length and 2.6 (2.0–3.3) µm in width, with 2–3 coil polar tubules. Valvular protrusions were observed, associated with the tips of the polar capsules. Molecular analysis based on the SSU rDNA sequences indicated that the two novel Ellipsomyxa species were distinct from all other sequences deposited in the GenBank database. The phylogenetic trees clustered E. plagioscioni n. sp. as a basal species of a lineage of the marine/estuarine Ellipsomyxa, while E. paraensis n. sp. clustered together with other Amazonian species.

EllipsomyxaKøie属的种，2003年寄生于世界各地的大部分海水和咸鱼中。在本研究中，我们描述了两种新的Ellipsomyxa物种：Ellipsomyxa plagioscioni n。sp。寄生了淡水鱼Plagioscion squamosissimus（Sciaenidae）的胆囊，但通常在亚马逊河口环境的微咸水中发现；以及Ellipsomyxa paraensis n。sp。感染C鱼（丽鱼科鱼），一种严格的淡水鱼。宿主标本是从巴西帕拉州圣塔雷姆市的亚马逊河和塔帕霍斯河中捕获的。这项研究是结合基于形态，生物学和SSU rDNA的系统发育来进行的，这表明中南部中新世时代的海侵是适应和辐射这些刺胞寄生虫的途径。淡水环境。发现散在的胞浆虫和成熟的粘孢子都自由漂浮在胆汁中。在瓣膜和缝合视图中，两种物种的成熟粘孢子均呈椭圆形，在垂直于横向缝合线平面的方向上细长的光滑瓣膜伸长。斜纹小球藻。sp。粘孢子的长度为11.1（10.2–12.8）µm，宽度为6.6（5.6–7.6）µm。两个呈梨形的极性小囊在相对的侧面上放电，距缝合线和孢子末端都有一定距离，长度为3.8（3.2–4.4）µm，宽度为2.8（2.3–3.3）µm，带有5–6个盘管极性小管。Ellipsomyxa paraensis ñ。sp。粘孢子的长度为11.5（10.5–12.4）µm，宽度为7.5（6.6–8.6）µm。两个梨形极囊，在相对侧从缝合线和孢子末端排出一定距离，长度为3.2（2.1–3.9）µm，宽度为2.6（2.0–3.3）µm，带有2–3个螺旋极管。观察到瓣膜突出，与极膜的尖端有关。基于SSU rDNA序列的分子分析表明，这两种新型Ellipsomyxa物种不同于GenBank数据库中保存的所有其他序列。系统发育树聚集了斜纹夜蛾E. plagioscioni n。sp。作为海洋/河口Ellipsomyxa世系的基础物种，而E. paraensis n。sp。与其他亚马逊物种聚集在一起。