Anthocephalum Linton, 1890

Anthocephalum Linton, 1890 View in CoL amended

syn. Pararhinebothroides Zamparo, Brooks, & Barriga, 1999 ; Alveobothrium Boudaya, Neifar & Euzet, 2018 .

Worms weakly craspedote, apolytic or euapolytic. Scolex with 4 bothridia and short or absent cephalic peduncle. Bothridia stalked, with numerous marginal loculi and single apical sucker; facial loculi present or absent. Proximal surfaces of marginal loculi with acicular filitriches and with or without scolopate spinitriches, or with capilliform filitriches and narrow gladiate spinitriches; proximal non-locular surfaces of bothridia with acicular filitriches, and with or without narrow gladiate spinitriches; distal bothridial surfaces with acicular or capilliform filitriches and small gladiate spinitriches. Mature proglottids longer than wide. Testes entirely pre-ovarian, medullary; postporal field of testes lacking. Genital pores lateral, usually in posterior half of proglottid; genital atrium present. Internal seminal vesicle present or absent. Vagina sinuous, opening into genital atrium anterior to cirrus sac. Ovary posterior in position, H-shaped in frontal view, tetralobed in cross-section. Vitellaria follicular; vitelline follicles in 2 lateral bands; each band consisting of 1 or more columns of vitelline follicles, uninterrupted by ovary, or partially or completely interrupted by ovary, and interrupted or uninterrupted by genital pore. Uterus median, ventral, sacciform, extending from level of cirrus sac to stopping short of anterior limit of field of testes or to anterior margin of proglottid. Parasites of stingrays ( Myliobatiformes ) and electric rays ( Torpediniformes ).

Remarks: The revision of the Anthocephalum diagnosis was necessary to accommodate the unique scolex morphology of Anthocephalum grabatum n. comb., and Anthocephalum zarzisense n. comb., which possess facially loculated bothridia. The incorporation of these two species raises the total number of species within the genus to 30 ( Boudaya et al., 2018; Herzog and Jensen, 2018). Alveobothrium was established by Boudaya et al. (2018) to include species morphologically akin to Anthocephalum , but characterized by a scolex bearing staggered facial loculi arranged in multiple rows, a trait absent in Anthocephalum sensu stricto ( Ruhnke et al., 2015; Herzog and Jensen, 2018). Despite this distinguishing feature, Alveobothrium shares all other morphological characteristics with Anthocephalum , leading the authors to recognize Alveobothrium on the basis of its unique scolex morphology alone.

Phylogenetic analyses have previously supported the inclusion of tapeworms with varying scolex morphologies within a single genus of chondrichthyan parasites (e.g., Reyda et al., 2016; Trevisan et al., 2017; Caira et al., 2020). For example, Anindobothrium lisae Marques, Brooks & Lasso, 2001 , a parasite of freshwater stingrays, lacks facial loculi and longitudinal septa, which contrast with marine species of the same genus that exhibit these features. Despite these differences, Anindobothrium lisae shares key morphological traits with other members of the genus and is confirmed by molecular evidence to belong to Anindobothrium ( Trevisan et al., 2017) . Additionally, in a recent redefinition of Scyphophyllidium Woodland, 1927 ( Phyllobothriidea ), Caira et al. (2020) examined six genera with similar proglottid anatomy and unique ultrastructural characteristics but divergent bothridial morphologies, such as the presence or absence of apical suckers and loculi. They concluded that bothridial morphology represented intra-genus diversity and proposed synonymizing the six genera under Scyphophyllidium , organizing the species into eight groups based on bothridial morphology. Similarly, despite differences in bothridial morphology, species of Anthocephalum and Alveobothrium display comparable proglottid anatomies. In our phylogenetic analysis, the positioning of Alveobothrium grabatum alongside other Anthocephalum species is strongly supported. This result, when considered in conjunction with the aforementioned evidence, substantiates the proposed taxonomic synonymy.