Carina, a sharp extension of the basal margin in some chitinozoans recalling a “skirt”, is a primary character used for classifying chitinozoans at the genus level. However, little is known about this structure. In this study, we present new observations on the carina ultrastructure in the chitinozoan genus Cyathochitina that was investigated by using novel imaging techniques on three-dimensional specimens collected mainly from eastern Baltoscandia. The results show that the carina is loosely filled by sponge-like fibers with chemical compositions similar to those of the main vesicle layers. Cyathochitina is the dominant genus responsible for the taxonomic diversity of carina-bearing species, and it reached a diversity peak in the late Darriwilian. Palaeogeographically, the occurrences of Cyathochitina in the eastern Baltic region are reconstructed on the basis of data collected from 24 drillcores, suggesting links with sea-level fluctuations. The presence and morphology of the carina is interpreted as an adaptive life strategy with two benefits. First, the carina strengthened the basal firmness and reduced the weight of the chitinozoan vesicle by filling it with spongy fibrils. Second, computational fluid dynamics (CFD) analysis suggests that the formation of the carina might have improved the hydrodynamic properties and floating ability of the vesicle by dispersal in different hydrodynamic regimes.

隆鼻（carina）是一些奇偶动物的基缘的急剧延伸，使人联想到“裙子”，它是在属水平上对奇脱奇动物进行分类的主要特征。但是，对该结构知之甚少。在这项研究中，我们就在几丁虫属隆突超微结构提出了新的意见Cyathochitina由使用上主要是收集来自Baltoscandia东部三维标本新型成像技术研究。结果表明，隆突被海绵状纤维松散填充，其化学成分与主要囊泡层的化学成分相似。矢车菊属是负责嘉里纳鱼类物种分类学多样性的主要属，在达里维利后期晚期达到了多样性高峰。在古地理上，波罗的海东部地区的连翘纲发生是根据从24个钻芯收集的数据重建的，这暗示了与海平面波动的联系。隆突的存在和形态被解释为具有两个好处的适应性生活策略。首先，隆突通过填充海绵状原纤维而增强了基层牢固性并减轻了几丁质囊泡的重量。其次，计算流体动力学（CFD）分析表明，隆起的形成可能通过分散在不同的流体动力学状态中而改善了囊的流体动力学特性和漂浮能力。