Parasites are ubiquitous in extant ecosystems but rarely preserved in the geological record, especially parasitic worms (helminths). One such group is Cestoda (tapeworms), a specialized endoparasitic group of platyhelminths (flatworms). They have a complex lifecycle with at least two hosts, infecting all major groups of vertebrates. However, their fossil record is extremely sparse due to their soft tissue and concealed habitats, with the only widely accepted example before the Quaternary being eggs discovered in a shark coprolite from the Permian. The lack of body fossils greatly hampers our understanding of their early evolution. We report a slender, armed fossil from mid-Cretaceous Kachin (Myanmar) amber (ca. 99 Ma). This fossil displays unique external (armature pattern) and internal (partially invaginated tentacle and rootless hooks) features that are most consistent with the tentacles of extant trypanorhynch tapeworms that parasitize marine elasmobranchs (mainly sharks and rays). Our study thus probably provides not only the first partial body fossil of a tapeworm, but also arguably the most convincing body fossil of a flatworm. In addition, the exquisite invaginated tentacle inside the fossil highlights that amber can preserve the internal structure of helminths. Remarkably, nearly all extant trypanorhynchs are endoparasites of marine elasmobranchs, thus our study provides an exceptional example of a marine endoparasite trapped in terrestrial amber.

中文翻译：

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白垩纪琥珀中保存完好的海洋绦虫触手


寄生虫在现存的生态系统中无处不在，但很少保存在地质记录中，尤其是寄生蠕虫（蠕虫）。其中一个类群是 Cestoda（绦虫），这是一种专门的内寄生扁形动物类群（扁形虫）。它们具有复杂的生命周期，至少有两个宿主，感染所有主要脊椎动物群体。然而，由于它们的软组织和隐蔽的栖息地，它们的化石记录极其稀疏，第四纪之前唯一被广泛接受的例子是在二叠纪的鲨鱼粪化石中发现的卵。尸体化石的缺乏极大地阻碍了我们对其早期进化的理解。我们报告了一块来自白垩纪中期克钦邦（缅甸）琥珀（约 99 Ma）的细长武装化石。该化石显示出独特的外部（电枢图案）和内部（部分内陷的触手和无根钩）特征，与现存寄生于海洋软骨鱼（主要是鲨鱼和鳐鱼）的锥虫绦虫的触手最为一致。因此，我们的研究可能不仅提供了第一个绦虫的部分身体化石，而且可以说是最令人信服的扁虫身体化石。此外，化石内部精美的内陷触手凸显了琥珀可以保存蠕虫的内部结构。值得注意的是，几乎所有现存的锥虫都是海洋软骨鱼类的体内寄生虫，因此我们的研究提供了一个捕获在陆地琥珀中的海洋体内寄生虫的特殊例子。