We describe a new genus and species of blood‐dwelling apostome ciliate, Lynnia grapsolytica n. gen., n. sp. (Apostomatida: Colliniidae). A distinct kinety “hook” pattern on the tomite’s posterior ventral face, coupled with its marine habitat and use of a decapod host, readily distinguishes this ciliate from all known colliniids. We detected the parasite in ~12% of Pachygrapsus crassipes (Brachyura: Grapsidae) crabs in a California estuary and confirmed its presence at a Baja California rocky intertidal site. As existing methods failed to adequately stain this ciliate, we developed a new miniaturized silver carbonate impregnation staining method that produced excellent somatic and nuclear stains in all five observed cell types. A possibly unique trait is the active invagination of the tropho‐tomont’s anterior to form a temporary “pseudocytopharynx,” likely used for feeding. Histological examination revealed that the ciliate invaded and damaged skeletal muscle, the heart, connective tissues, and gonads. Survivorship analysis indicated that infected crabs experienced 2.6 times greater daily mortality than uninfected crabs. Laboratory and field experimental infection attempts failed, suggesting a complex life cycle with outside‐host development. Phylogenetic analysis at the 18S and COI loci confirmed the ciliate's placement in the Colliniidae. We emend the diagnosis of Family Colliniidae.

中文翻译：

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Lynnia grapsolytica n. gen, n. sp. (Ciliophora: Apostomatida: Colliniidae)，一种致命的螃蟹血液寄生虫，具有新型的假细胞

我们描述了一种新的血栖后体纤毛虫属和种，Lynnia grapsolytica n。gen., n. sp. (Apostomatida: Colliniidae)。tomite 后腹面的一个独特的运动“钩”图案，加上它的海洋栖息地和使用十足目宿主，很容易将这种纤毛虫与所有已知的胶体动物区分开来。我们在大约 12% 的Pachygrapsus crassipes 中检测到了寄生虫（Brachyura：Grapsidae）在加利福尼亚河口的螃蟹并证实它存在于下加利福尼亚州的岩石潮间带地点。由于现有方法未能充分染色这种纤毛虫，我们开发了一种新的小型化碳酸银浸渍染色方法，该方法在所有五种观察到的细胞类型中产生了出色的体细胞和核染色。一个可能的独特特征是滋养层的前部主动内陷，形成一个临时的“假细胞咽”，可能用于进食。组织学检查显示纤毛虫侵入并损伤骨骼肌、心脏、结缔组织和性腺。存活率分析表明，受感染的螃蟹的每日死亡率是未受感染的螃蟹的 2.6 倍。实验室和现场实验感染尝试失败，表明具有外部宿主发育的复杂生命周期。18S 和 COI 位点的系统发育分析证实了纤毛虫在 Colliniidae 中的位置。我们修正了科利尼科的诊断。