Gelatinous zooplankton are essential components of healthy ecosystems. Given their characteristic life cycle, ecological aspects and adaptability to a variety of oceanic conditions, these organisms are considered indicators of climate change, having particular advantages relative to other taxa. Citizen science initiatives are becoming increasingly frequent, providing data that are otherwise difficult to collect and interesting results for different taxa worldwide, allowing for example the detection of new occurrences. The ongoing citizen science program GelAvista, running since 2016, gathers data reported by observers on jellyfish occurrences in Portuguese waters, in the north-eastern Atlantic. The program has enhanced the knowledge of these organisms, providing data on biodiversity, and the dynamics of their distribution and abundance. Particular sightings of hydromedusae were received through GelAvista for mainland Portugal, close to the Tagus River, in the Lisbon Bay region. The species was morphologically and molecularly identified as Odessia maeotica, comprising its first reported occurrence in the Lisbon Bay. The details on the occurrence of the species are provided and discussed given the current knowledge of the species.

凝胶状浮游动物是健康生态系统的重要组成部分。鉴于其独特的生命周期、生态方面和对各种海洋条件的适应性，这些生物被认为是气候变化的指标，相对于其他类群具有特殊的优势。公民科学倡议变得越来越频繁，为世界各地不同的分类群提供难以收集的数据和有趣的结果，例如允许检测新的事件。正在进行的公民科学计划 GelAvista 自 2016 年开始运行，收集观察者报告的有关大西洋东北部葡萄牙水域水母发生情况的数据。该计划增强了对这些生物体的了解，提供了有关生物多样性及其分布和丰度动态的数据。通过 GelAvista 在葡萄牙大陆里斯本湾地区靠近塔霍河的地方收到了水螅水母的特别目击报告。该物种在形态学和分子学上被鉴定为Odessia maeotica，这是其首次报告出现在里斯本湾。鉴于该物种的当前知识，提供并讨论了该物种出现的详细信息。