Warren Micah B, Dutton Haley R, Whelan Nathan V, Yanong Roy P E, Bullard Stephen A
1 School of Fisheries, Aquaculture, & Aquatic Sciences, Auburn University, 203 Swingle Hall, Auburn, Alabama 36849.
2 Southeast Conservation Genetics Lab, Warm Springs Fish Technology Center, United States Fish and Wildlife Service, 203 Swingle Hall, Auburn, Alabama 36849.
J Parasitol. 2019 Apr;105(2):237-247.
The hemocoel of 26 of 30 (86%) eastern grass shrimps, Palaemon paludosus (Gibbes, 1850) (Decapoda: Palaemonidae), captured during June 2017 from several freshwater lakes near Leesburg and Lake Kissimmee, Florida, was infected by juveniles of a nematode species (Mermithidae sp.). Some infected eastern grass shrimps were preserved whole for histopathology, whereas others were dissected to excise parasitic juvenile nematodes, and still others were kept alive in glass aquaria such that post-parasitic (emerged) juvenile nematodes could be opportunistically observed alive and ultimately preserved. Parasitic and post-parasitic juvenile nematodes had cuticle cross-fibers, cephalic papillae, cup-shaped amphids, a horn-shaped vagina, a trophosome, and a caudal appendage, which collectively diagnosed them as Mermithidae sp. They differed from those of nematomorphs (Nematomorpha) by lacking 4 giant cells anteriorly, tegumental bristles, scale or plate-like areoles, a bifurcate or trifurcate posterior end, and an anus. A phylogenetic analysis of the small subunit rDNA (18S) that included all of the available mermithid sequences corresponding to morphologically diagnosed specimens recovered Mermithidae sp. within the clade of mermithids and sister to Ovomermis sinensis Chen, Jian, and Ren, 1991 . This is the first record of a mermithid infection in a decapod and first report of a mermithid infection in an aquatic crustacean from North America (another mermithid infects a terrestrial isopod there). The high prevalence of infection and the multiple geographic localities harboring infected eastern grass shrimps indicated that these infections were not spurious. Because no other decapod is confirmed as a mermithid host, we suspect that these specimens likely represent a new species with a life cycle worth studying, since none for a mermithid involving a decapod nor a crustacean has been elucidated to date. We also provide a table of all mermithid and nematomorph infections in crustaceans.
2017年6月，从佛罗里达州利斯堡和基西米湖附近的几个淡水湖捕获的30只东部草虾（Palaemon paludosus，(Gibbes, 1850)，十足目：长臂虾科）中，有26只（86%）的血腔被一种线虫（索科线虫属）的幼虫感染。一些受感染的东部草虾被完整保存用于组织病理学研究，另一些则被解剖以切除寄生的线虫幼虫，还有一些被养在玻璃水族箱中，以便可以机会性地观察到寄生后（羽化）的线虫幼虫存活情况并最终保存下来。寄生和寄生后的线虫幼虫具有角质层交叉纤维、头部乳突、杯状化感器、角状阴道、营养体和尾附器，这些特征共同将它们诊断为索科线虫属。它们与线形动物的区别在于，前端没有4个巨大细胞、体表刚毛、鳞片或板状小窝、后端分叉或三分叉以及肛门。对小亚基核糖体DNA（18S）进行的系统发育分析，包括所有与形态学诊断标本相对应的可用索科线虫序列，结果显示索科线虫属在索科线虫类群中，且与1991年的中华卵索线虫（Ovomermis sinensis Chen, Jian, and Ren）是姐妹关系。这是十足目中索科线虫感染的首次记录，也是北美水生甲壳类动物中索科线虫感染的首次报道（另一种索科线虫感染那里的一种陆生等足类动物）。感染的高发生率以及多个地理区域存在受感染的东部草虾表明这些感染并非偶然。由于没有其他十足目动物被确认为索科线虫的宿主，我们怀疑这些标本可能代表一个生命周期值得研究的新物种，因为迄今为止尚未阐明涉及十足目动物或甲壳类动物的索科线虫的生命周期。我们还提供了甲壳类动物中所有索科线虫和线形动物感染情况的表格。
