The northern cottonmouth, Agkistrodon piscivorus (Lacépède, 1789) (Viperidae: Crotalinae), occurs in the southeastern United States and is one of the few semiaquatic vipers in the world. Three proteocephalid tapeworms of the genus OphiotaeniaLa Rue, 1911 (Cestoda), have been described from this venomous snake. A critical evaluation of type specimens and tapeworms recently collected from A. piscivorus has revealed that only 2 species, Ophiotaenia marenzelleri (Barrois, 1898) and Ophiotaenia grandisLa Rue, 1911 (new synonym Ophiotaenia agkistrodontis [Harwood, 1933]), are specific parasites of this crotaline viper; both species are redescribed here. Ophiotaenia grandis was originally described from a mixture of 2 species: ‘true’ O. grandis, which is indistinguishable from O. agkistrodontis described 22 yr later and thus considered to be a junior synonym of O. grandis, and O. marenzelleri. Ophiotaenia marenzelleri, also reported from the pygmy rattlesnake, Sistrurus miliarius (Linnaeus, 1766), is a larger tapeworm with a massive scolex, a large cirrus sac, a very large, annular vaginal sphincter near the equatorial gonopore, and an oval, 3-layered embryophore surrounded by a nearly square hyaline outer membrane. Ophiotaenia grandis is much smaller and more slender and has a narrower scolex, a smaller cirrus sac and vaginal sphincter, a 2-layered embryophore, and a distinctly pre-equatorial gonopore. In addition to O. marenzelleri and O. grandis, other Ophiotaenia species typical of semiaquatic snakes (Colubridae: Natricinae) may be present in the northern cottonmouth, which serves only as a postcyclic or occasional host. There is also a tabular summary of 18 species of Ophiotaenia from semiaquatic snakes worldwide, with information on their hosts, distribution, and taxonomically important characters, including key measurements.

北部棉口蝰蛇Agkistrodon piscivorus (Lacépède, 1789)（蝰蛇科：Crotalinae）分布于美国东南部，是世界上为数不多的半水生毒蛇之一。从这条毒蛇中描述了三种Ophiotaenia La Rue, 1911 (Cestoda) 属的原头绦虫。对最近从A. piscivorus收集的模式标本和绦虫进行的严格评估表明，只有 2 个物种，Ophiotaenia marenzelleri (Barrois, 1898) 和Ophiotaenia grandis La Rue, 1911（新同义词Ophiotaenia agkistrodontis [Harwood, 1933]）是特定寄生虫这条响尾蛇毒蛇；此处重新描述了这两个物种。Ophiotaenia grandis最初被描述为 2 个物种的混合物：“真正的” O. grandis ，与 22 年后描述的O. agkistrodontis没有区别，因此被认为是O. grandis和O. marenzelleri的初级同义词。Ophiotaenia marenzelleri也来自侏儒响尾蛇Sistrurus miliarius (Linnaeus, 1766)，是一种较大的绦虫，具有巨大的头节、大卷囊、靠近赤道生殖孔的非常大的环形阴道括约肌和椭圆形 3-层状胚芽被近乎方形的透明外膜包围。Ophiotaenia grandis更小、更细长，具有更窄的头节、更小的卷囊和阴道括约肌、2 层胚芽和明显的前赤道性生殖孔。除了O. marenzelleri和O. grandis之外，其他典型的半水生蛇类（游蛇科：Natricinae）蛇类也可能存在于北部棉口蛇中，其仅作为后周期或偶尔的宿主。还有来自世界各地半水生蛇的 18 种Ophiotaenia的表格摘要，其中包含有关其寄主、分布和重要分类特征（包括关键测量值）的信息。