摘要：AbstractHysterothylaciumspecies 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 genusHysterothylacium(Ward and Magath, 1917) are morphologically described from the digestive tract ofArgyrops spinifer, genetically characterized and their relationship with related taxa are compared and discussed. The former species (Hysterothylacium reliquensNorris 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 [cytochromecoxidase 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 asH. reliquensbased 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 generaRaphidascaris,Contracaecum,andHysterothylacium. This study demonstrated that selected gene regions ofH. reliquensyielded 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.
