Department of Biology, University of Vermont, Burlington, Vermont 05405.
Department of Plant and Soil Science, University of Vermont, Burlington, Vermont 05405.
J Parasitol. 2023 Mar 1;109(2):56-64. doi: 10.1645/22-66.
Apolocystis bosanqueti n. sp., a parasite of an important invasive earthworm in North America, Amynthas agrestis, is described from a site in northern Vermont. The earthworm host follows an annual life cycle in Vermont, so the entire life cycle of the parasite can be observed in 7 mo. In spring, the parasites were first seen in juvenile worms as paired gamonts (suggesting precocious association). These paired gamonts mature into gametocytes that form an opaque structure, with a thick gelatinous envelope (epicyst), that becomes full of zygotes. The resulting gametocyst becomes packed with ∼105 fusiform oocysts. The mature orbicular gametocysts are large (∼1 mm in diameter) and visible to the naked eye through the body wall of the host's anterior segments. The new species most resembles Apolocystis herculea described from many lumbricid earthworm species in Europe but differs from that parasite because Ap. herculea infects the intestinal wall in the posterior of the host rather than the anterior segments. A survey of 9 other earthworm species sympatric with Am. agrestis revealed that only Amynthas tokioensis, also an invasive species, was infected with Ap. bosanqueti, albeit much less commonly. Diagnosis for the family Monocystidae is problematic because cardinal characters are lacking, and the commonly cited character, a trophozoite with no anterior differentiation, is violated in most genera placed in the family. For the first time, a molecular phylogeny is presented that includes 3 genera of monocystids with diverse cell morphology (including the new species) and supports the monophyly of the family. The only morphological character that may be used to diagnose the Monocystidae is the morphology of oocysts, which are fusiform with extended terminal tips. A comparison of oocysts from 7 parasites recovered from local earthworms, including from 3 monocystid species in the phylogeny, confirms the utility of this diagnostic trait. The 2 hosts of the new species were most likely introduced from Japan, so the range of Apolocystis likely extends into East Asia.
伯桑奎氏单房棘口吸虫，一种寄生在北美洲重要入侵蚯蚓（美国野蛞蝓）体内的寄生虫，在佛蒙特州北部的一个地点被描述。在佛蒙特州，蚯蚓宿主遵循一年的生命周期，因此寄生虫的整个生命周期可以在 7 个月内观察到。在春季，寄生虫首次在幼年蚯蚓中以成对的滋养体形式出现（提示早熟关联）。这些成对的滋养体成熟为配子体，形成不透明的结构，具有厚厚的胶状包膜（外囊），充满了合子。由此产生的配子囊充满了约 105 个梭形卵囊。成熟的球形配子囊很大（直径约 1 毫米），可以通过宿主前节的体壁肉眼看到。这个新物种最类似于从欧洲许多蚯蚓物种中描述的阿氏棘口吸虫，但与该寄生虫不同，因为阿氏棘口吸虫感染宿主的后肠壁而不是前节。对与美国野蛞蝓共生的 9 种其他蚯蚓物种的调查显示，只有同为入侵物种的东京野蛞蝓感染了伯桑奎氏单房棘口吸虫，尽管感染程度要低得多。由于缺乏主要特征，单房科的诊断存在问题，并且通常引用的特征，即没有前部分化的滋养体，在大多数归入该科的属中都被违反。这是首次提出包括具有不同细胞形态（包括新物种）的 3 个单房科属的分子系统发育，支持该科的单系性。唯一可能用于诊断单房科的形态特征是卵囊的形态，卵囊呈梭形，末端有延伸的尖端。从当地蚯蚓中回收的 7 种寄生虫的卵囊的比较，包括系统发育中的 3 种单房科物种，证实了这种诊断特征的有用性。新种的 2 个宿主很可能是从日本引进的，因此阿氏棘口吸虫的分布范围可能延伸到东亚。
