The role of invertebrates in some acanthocephalan life cycles is unclear because juvenile acanthocephalans are difficult to identify to species using morphology. Most reports suggest acanthocephalans from turtle definitive hosts use ostracods as intermediate hosts and snails as paratenic hosts. However, laboratory studies of the life cycle suggest that ostracods and snails are both required hosts in the life cycle. To elucidate the role of ostracods and snails in acanthocephalan life cycles better, we collected 558 freshwater snails of 2 species, including Planorbella cf. Planorbella trivolvis and Physa acuta, from 23 wetlands in Oklahoma, U.S.A., and examined them for acanthocephalan infections. Additionally, we examined 37,208 ostracods of 4 species, Physocypria sp. (morphotype 1), Cypridopsis sp., Stenocypris sp., and Physocypria sp. (morphotype 2) for juvenile acanthocephalans from 2 wetlands in Oklahoma. Juvenile acanthocephalans were morphologically characterized, and the complete internal transcribed spacer (ITS) region of nuclear rDNA was sequenced from acanthocephalans infecting 11 ostracod and 13 snail hosts. We also sampled 10 red-eared slider turtles, Trachemys scripta elegans, and 1 common map turtle, Graptemys geographica, collected from Oklahoma, Arkansas, and Texas and recovered 1,854 adult acanthocephalans of 4 species. The ITS of 17 adult acanthocephalans of 4 species from turtle hosts were sequenced and compared to juvenile acanthocephalan sequences from ostracod and snail hosts from this study and GenBank to determine conspecificity. Of the 23 locations sampled for snails, 7 (30%) were positive for juvenile acanthocephalans in the genus Neoechinorhynchus. The overall prevalence and mean intensity of acanthocephalans in Planorbella cf. P. trivolvis and P. acuta were 20% and 2 (1–6) and 2% and 1 (1), respectively. In contrast, only 1 of 4 species of ostracods, Physocypria sp. (morphotype 1), was infected with larval/juvenile Neoechinorhynchus spp. with an overall prevalence of 0.1% and a mean intensity of 1 (1–2). Although 4 species of acanthocephalans infected turtle definitive hosts, including Neoechinorhynchus chrysemydis, Neoechinorhynchus emydis, Neoechinorhynchus emyditoides, and Neoechinorhynchus pseudemydis, all the ITS sequences from cystacanths infecting snail hosts were conspecific with N. emydis. In contrast, the ITS sequences from larval/juvenile acanthocephalans from ostracods were conspecific with 2 species of acanthocephalans from turtles (N. emydis and N. pseudemydis) and 1 species of acanthocephalan from fish (Neoechinorhynchus cylindratus). These results indicate that N. emydis infects freshwater snails, whereas other species of Neoechinorhynchus appear not to infect snail hosts. We document new ostracod and snail hosts for Neoechinorhynchus species, including the first report of an ostracod host for N. pseudemydis, and we provide novel molecular barcodes that can be used to determine larva, juvenile, and adult conspecificity of Neoechinorhynchus species.

无脊椎动物在一些棘头动物生命周期中的作用尚不清楚，因为幼年棘头动物很难通过形态学识别物种。大多数报告表明，来自龟终宿主的棘头动物使用介形虫作为中间宿主，而蜗牛作为寄生虫宿主。然而，生命周期的实验室研究表明，介形虫和蜗牛都是生命周期中必需的宿主。为了更好地阐明介形虫和蜗牛在棘头动物生命周期中的作用，我们收集了 2 个物种的 558 只淡水蜗牛，包括Planorbella cf。来自美国俄克拉荷马州 23 个湿地的Planorbella trivolvis和Physa acuta，并检查了它们的棘头动物感染情况。此外，我们还检查了 4 个物种的 37,208 只介形类动物，Physocypria sp。（形态型 1）、Cypridopsis sp.、Stenocypris sp. 和Physocypria sp.。（形态类型 2）来自俄克拉荷马州 2 个湿地的幼年棘头动物。对幼年棘头动物进行了形态学特征分析，并从感染 11 只介形类动物和 13 只蜗牛宿主的棘头动物中测序了核 rDNA的完整内部转录间隔区 ( ITS ) 区域。我们还从俄克拉荷马州、阿肯色州和得克萨斯州采集了 10 只红耳滑龟（Trachemys scripta elegans）和 1 只普通地图龟（Graptemys geoca），并回收了 4 个物种的 1,854 只成年棘头动物。在ITS对来自海龟宿主的 4 个物种的 17 只成年棘头动物进行测序，并与来自本研究和 GenBank 的介形类和蜗牛宿主的幼年棘头动物序列进行比较，以确定同种性。在对蜗牛进行采样的 23 个地点中，有 7 个（30%）对新棘爪龙属的幼年棘头动物呈阳性反应。Planorbella中棘头动物的总体流行率和平均强度cf。P. trivolvis和P. acuta分别为 20% 和 2 (1-6) 和 2% 和 1 (1)。相比之下，只有 4 种介形虫中的 1 种，Physocypria sp。（形态型 1），感染了幼虫/幼鱼Neoechinorhynchusspp. 总体患病率为 0.1%，平均强度为 1 (1-2)。尽管有 4 种棘头动物感染了龟最终宿主，包括Neoechinorhynchus chrysemydis、Neoechinorhynchus emydis、Neoechinorhynchus emyditoides和Neoechinorhynchus pseudemydis，但所有感染蜗牛宿主的囊棘鱼的ITS序列均与N. emydis同种。相比之下，来自介形类动物的幼体/幼年棘头动物的ITS序列与来自海龟的 2 种棘头动物（N. emydis和N. pseudemydis）和来自鱼类的 1 种棘头动物（圆柱新棘鱼）。这些结果表明N. emydis感染淡水蜗牛，而其他种类的Neoechinorhynchus似乎不感染蜗牛宿主。我们记录了Neoechinorhynchus物种的新介形虫和蜗牛宿主，包括首次报道N. pseudemydis的介形虫宿主，并且我们提供了可用于确定Neoechinorhynchus物种的幼虫、幼体和成虫同种性的新型分子条形码。