ABSTRACT. Rheodreissena Geda et al. 2018, a recently described genus of Dreissenidae, is represented by living species that inhabit inland freshwaters of Brazil and Venezuela. The type species of Rheodreissena is R. hoeblichi (Schütt 1991a) described from the lower Orinoco basin, Venezuela. Three species are added in this study: R. lopesi (Alvarenga & Ricci, 1989) from the Tocantins and Xingu basins; R. cordilineata n. sp. from the Madeira, Trombetas and Xingu basins, and R. xinguana n. sp. from the Tapajós and Xingu basins. Those three species are recorded from Volta Grande, the stretch of the Xingu River impacted by the Belo Monte dam complex. All Rheodreissena typically attach in shallow clusters to clean, rocky substrates associated with rapids in the main channels of large clear water rivers. Species of Rheodreissena are distinguished by aspects of shell morphology and soft anatomy that presumably reflect adaptations to a rheophilic lifestyle. In Xingu and Tocantins populations of Rheodreissena, larval broods were observed in the ctenidial (R. lopesi and R. xinguana) and pallial cavities of females (all three species). Examples of pallial broods included a few prodissoconch-1 (D-shaped) larvae in R. xinguana n. sp., 24 larvae/juveniles representing three different stages (prodissoconch 1 and 2, dissoconch) in R. cordilineata and up to 65 larvae/juveniles representing the same three stages in R. lopesi. In R. cordilineata and R. lopesi, the prodissoconch is attached to the parental mantle via a modified velum (adhesivelum), and dissoconchs attain lengths of 800 µm and 987 µm, respectively. For larvae brooded in the pallial cavity, a biphasic growth pattern was demonstrated statistically in R. lopesi and determined by observation in R. cordilineata. Juveniles are presumably released gradually into the environment at the crawl-away dissoconch stage. Biphasic brooding (ctenidial and pallial) was previously described for the European cave-dwelling dreissenid species Congeria kusceri; differences between brooding in Congeria and Rheodreissena are noted. Various morphological and lifehistory traits of species of Rheodreissena are summarized and compared to the other living species of Dreissenidae: Mytilopsis leucophaeata, M. sallei, Dreissena polymorpha, D. rostriformis (ex. bugensis), and the three nominal species of Congeria.

中文翻译：

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Rheodreissena（双壳壳纲：Veneroida：Dreissenidae）的形态学评估，更新了该属的诊断，两个新物种的描述，R. lopesi 的重新描述，以及对新世界德莱森纲幼虫育雏的首次描述

摘要。Rheodreissena Geda 等。2018 是最近描述的 Dreissenidae 属，以居住在巴西和委内瑞拉内陆淡水中的活物种为代表。Rheodreissena 的模式种是从委内瑞拉奥里诺科盆地下游描述的 R. hoeblichi (Schütt 1991a)。本研究中添加了三个物种： 来自 Tocantins 和 Xingu 盆地的 R. lopesi (Alvarenga & Ricci, 1989)；R.cordilineata n. sp. 来自 Madeira、Trombetas 和 Xingu 盆地，以及 R. xinguana n. sp. 来自 Tapajós 和 Xingu 盆地。这三个物种记录自Volta Grande，这是受Belo Monte 水坝影响的新古河段。所有 Rheodreissena 通常以浅层簇状附着在干净的岩石基底上，这些基底与大型清水河流的主要渠道中的急流有关。Rheodreissena 物种的特点是外壳形态和柔软的解剖结构，这可能反映了对嗜流变生活方式的适应。在Rheodreissena 的Xingu 和Tocantins 种群中，在雌性（所有三个物种）的ctenidial（R. lopesi 和R. xinguana）和苍白腔中观察到幼虫育雏。苍白幼虫的例子包括 R. xinguana n. 中的一些 prodissoconch-1（D 形）幼虫。sp.，24 只幼虫/幼虫代表 R.cordilineata 的三个不同阶段（prodissoconch 1 和 2，dissoconch），多达 65 只幼虫/幼虫代表 R. lopesi 的相同三个阶段。在 R. cordilineata 和 R. lopesi 中，prodissoconch 通过改良的帆 (adhesivelum) 附着在亲本地幔上，dissoconchs 的长度分别为 800 µm 和 987 µm。对于在苍穹内孵化的幼虫，在 R. lopesi 中统计证明了双相生长模式，并通过在 R.cordilineata 中观察确定。幼鱼可能在爬行分离阶段逐渐释放到环境中。双相育雏（ctenidial 和 pallial）先前已被描述为欧洲洞穴栖息的德莱森物种 Congeria kusceri；注意到 Congeria 和 Rheodreissena 育雏之间的差异。总结了 Rheodreissena 物种的各种形态和生活史特征，并与 Dreissenidae 的其他现存物种进行了比较：Mytilopsis leucophaeata、M. sallei、Dreissena polymorpha、D. rostriformis (ex. bugensis) 和 Congeria 的三个名义物种。幼鱼可能在爬行分离阶段逐渐释放到环境中。双相育雏（ctenidial 和 pallial）先前已被描述为欧洲洞穴栖息的德莱森物种 Congeria kusceri；注意到 Congeria 和 Rheodreissena 育雏之间的差异。总结了 Rheodreissena 物种的各种形态和生活史特征，并与 Dreissenidae 的其他现存物种进行了比较：Mytilopsis leucophaeata、M. sallei、Dreissena polymorpha、D. rostriformis (ex. bugensis) 和 Congeria 的三个名义物种。幼鱼可能在爬行分离阶段逐渐释放到环境中。双相育雏（ctenidial 和 pallial）先前已被描述为欧洲洞穴栖息的德莱森物种 Congeria kusceri；注意到 Congeria 和 Rheodreissena 育雏之间的差异。总结了 Rheodreissena 物种的各种形态和生活史特征，并与 Dreissenidae 的其他现存物种进行了比较：Mytilopsis leucophaeata、M. sallei、Dreissena polymorpha、D. rostriformis (ex. bugensis) 和 Congeria 的三个名义物种。