Hysterothylacium species are perhaps the most abundant and diverse group of marine ascaridoids; however, their life cycle and specific identification in larval stages are difficult. In this study, three members of the genus Hysterothylacium (Ward and Magath, 1917) are morphologically described from the digestive tract of Argyrops spinifer, genetically characterized and their relationship with related taxa are compared and discussed. The former species (Hysterothylacium reliquens Norris and Overstreet, 1975) (p = 10%) is mainly characterized by its large body (male 30.89, females 34.15 mm long), the shape of lips, the presence of lateral alae, a short caecum, and a long ventricular appendix, length of spicules, number and distribution of genital papillae, and tail tip with numerous spines. The other species [fourth (L4) and third (L3) larval stages] (p = 46.66, 26.66%, respectively) are mainly characterized by body length (18.21 and 6.20 mm long, respectively), distinct three lips for L4 and poorly developed for L3, a shorter caecum than the ventricular appendix, tail tip lacks any distinct cuticular projections. Molecular tools were done via sequencing and analyzing target regions of ribosomal [internal transcribed spacer (ITS) and small ribosomal DNA (18S)] and mitochondrial [cytochrome c oxidase subunit 1 (COX1)]. These sequences demonstrate discrimination at the species level and confirm the validity of species determined by morphological identification. All sequenced parasite samples were identified as H. reliquens based on nucleotide sequence comparisons with other ascaridoids. In these analyses, Raphidascarididae formed a sister group to Anisakidae with strong nodal support. On MP trees, a genus-specific cluster with a well-support value was delineated in genera Raphidascaris, Contracaecum, and Hysterothylacium. This study demonstrated that selected gene regions of H. reliquens yielded unique sequences (gbl MZ148786.1, MZ148788.1, and MZ148789.1) that confirmed its taxonomic position in Raphidascarididae. Therefore, morphological and molecular tools are important for accurate diagnosis of genus and species of ascaridoids.

Hysterothylacium物种可能是最丰富和多样化的海洋蛔虫类群。然而，它们的生命周期和幼虫阶段的具体鉴定是困难的。在这项研究中，从Argyrops spinifer的消化道中对Hysterothylacium属的三个成员（Ward 和 Magath，1917 年）进行了形态学描述，对其遗传特征进行了比较和讨论，并讨论了它们与相关分类群的关系。前种（Hysterothylacium reliquensNorris and Overstreet, 1975) (p = 10%) 的主要特征是其大体型（男性 30.89，女性 34.15 毫米长）、嘴唇形状、存在侧翼、短盲肠和长脑室阑尾，针刺的长度，生殖乳头的数量和分布，以及带有许多刺的尾尖。其他物种[第四（L4）和第三（L3）幼虫阶段]（分别为p = 46.66，26.66％）的主要特征是体长（分别为18.21和6.20毫米长），L4明显的三唇和发育不良对于 L3，盲肠比心室阑尾短，尾尖没有任何明显的角质层突起。分子工具是通过测序和分析核糖体 [内部转录间隔区 (ITS) 和小核糖体 DNA (18S)] 和线粒体 [细胞色素c氧化酶亚基 1 (COX1)]。这些序列证明了物种水平上的歧视，并证实了通过形态学鉴定确定的物种的有效性。根据与其他蛔虫的核苷酸序列比较，所有测序的寄生虫样本均被鉴定为H. reliquens。在这些分析中，Raphidascarididae 与 Anisakidae 形成了一个具有强大节点支持的姐妹群。在MP树，一个良好的支持值属特异性集群中属被划定Raphidascaris，Contracaecum，和宫脂。该研究表明，H. reliquens 的选定基因区域产生了独特的序列（gbl MZ148786.1、MZ148788.1 和 MZ148789.1），证实了它在蛲虫科中的分类位置。因此，形态学和分子学工具对于蛔虫属和种的准确诊断非常重要。