The tapewormGyrocotyle discoveryi，，，，an internal parasite of the deep-sea ‘rat fish’Hydrolagus mirabilis。（照片来源：R。A. Bray）

tape虫可能是最古老的寄生虫类型的类型，其长长，分割，肠道的成年形式首先是由古希腊人描述的。像其他寄生虫（例如Flukes）一样，它们也非常适合强制性的寄生虫生活方式，并且几乎无法从其自由活动的扁虫表兄弟所识别。

As adults, they live in the intestines of vertebrates where they absorb food directly through their skin. Thus while flatworms typically have simple, blind guts lacking an anus, tapeworms have dispensed with the gut altogether, letting their host break down nutrients for them.

同时，他们的每个细分市场（根据物种的数量为3至1000）都包含一组完整的雄性和女性生殖器官（即雌雄同体）。因此，超过95％的tape虫成人身体致力于产生鸡蛋！这些鸡蛋最终从肠中释放到环境中，但是要成为成年人，它们至少需要另外一位宿主（有时是两个或三个） - 中间宿主 - 幼虫变成非细分的少年蠕虫，准备好在脊椎动物宿主中开始性发展，然后重新开始周期。

Putting the tape in tapeworms

但是，我们都认识到的tape虫形式从何而来？碰巧的是，即使在今天，并非所有的tape虫都被细分了，很明显，增加后代数量的适应性是其进化中相对较新的功能。

Without a fossil record there is effectively no direct evidence of tapeworm ancestry, but we do know from comparative studies of both anatomy and genetic sequences that the ‘true’ tapeworms (the group that includes all segmented species) have two extant (living) evolutionary tapeworm cousins. These two independent lineages each contain only a handful of species which share fundamental underlying characteristics of ‘true’ tapeworms, but otherwise bear little outward resemblance.

这些谱系之一是陀螺仪，以其特征性的“玫瑰花塞”器官命名（请参见顶部的图像）。它们是深海嵌合体或Ratfishes的寄生虫，与鲨鱼和射线一起包含软骨鱼。像真正的tape虫一样，成年陀螺仪生活在宿主的肠道中，他们得到营养。但是，它们没有分割，与扁虫通常不同，并不是特别平坦！

尽管自1800年代后期以来就知道了，但在过去的150年中，很少有有关该异常群体的新物种或其他报告发表。但是，在2020年我们报道了两个新物种来自北大西洋收集的嵌合体。

不常见的寄生虫……你ncommonly普遍

Whilst as a group gyrocotylideans are uncommon compared to the huge diversity of ‘true’ tapeworms (estimated to include more than 20,000 species), as individuals they are uncommonly common in their host group, with the percent of ratfishes infected reaching near 100% in some surveys.

Thus should you have the chance to collect and dissect a ratfish, the chances of finding a gyrocotylidean are high. Unfortunately, sampling from the deep-sea is itself a rare opportunity and of the known ratfish species, most are seldom encountered. The present study was based on collections in the North-East Atlantic made over three years providing the opportunity to investigate the presence of gyrocotylideans in two species of ratfishes never previously examined, revealing two new species of parasite.

足够的生存

Chimaeras are a relictual group of cartilaginous fishes whose diversity is known from the fossil record to have been far greater in the distant past. Although they rarely play host to ‘true’ tapeworms, their evolutionary cousins, the sharks and rays, play host to a significant part of the diversity of true tapeworms. As specialist parasites of chimaeras, gyrocotylideans also appear to be a relictual group, although their past diversity is not likely knowable.

Their contemporary diversity consists of a single known genus (Gyrocotyle）represented by a handful of named species, none of which can be distinguished on the basis of anatomy. Whether the group is really represented by a single, widespread species has long been debated.

The very deep sea is a highly stable environment compared to land – and in the relative absence of strong, dynamic selective forces, ‘survival of the adequate’ may be a better model than ‘survival of the fittest’ in explaining deep sea communities and their potential for relative stasis, compared to communities near the surface and on land.

However, while gyrocotylidean tapeworms are highly uniform in their appearance, the small amount of sequence data that have started to accumulate suggest that there is a significant amount of divergence among parasites sampled from different geographic areas and host species. Accumulating such divergence suggests that the parasites are genetically isolated by geography, host ecology and/or other factors. However, if this were the case, we would expect it to eventually translate into differences in their appearance (i.e. phenotype) as well, as genetic ‘drift’ will occur even in the absence of pressures caused by changes in the environment. Explaining the contemporary diversity of these unusual tapeworms will surely require a better understanding not only of their genetics, but also of the enigmatic ecology of their deep sea hosts.

2020年以来十个非凡的海洋新物种之一

As for previous years, the World Register of Marine Species (蠕虫）has again released theannual list of the top-ten marine speciesdescribed by researchers during the year 2020 to coincide with World Taxonomist Appreciation day (March 19th)!Gyrocotyle haffii，，，，or ‘Haffi’s Upside-Down Tapeworm”,选择其中十大物种。This new species is named in honour of Professor Harford ‘Haffi’ Williams in recognition of his contribution to the understanding of this group of tapeworms.