Integrative taxonomy in action: a new genus of phyllobothriid tapeworms (Cestoda: Phyllobothriidea), with insights on potential transmission pathways and influences of environmental gradients on diversity patterns of the group

Abstract

Originally described from the bluntnose sixgill shark, Hexanchus griseus (Bonnaterre), Phyllobothrium sinuosiceps Williams, 1959 (Cestoda: Phyllobothriidea) is apparently a common parasite of this elasmobranch host. However, reports of this species are limited, and its morphological characteristics remain poorly known. This study presents a molecular phylogenetic framework to reassess the taxonomic placement of this tapeworm within the order Phyllobothriidea. The results indicate a distinct phylogenetic position of Phyllobothrium sinuosiceps, leading to the erection of a new genus, Carrassoniella gen. nov., with Carrassoniella sinuosiceps comb. nov. as its type and only species. A comprehensive redescription of this enigmatic species is provided, with additional morphological data based on new specimens collected from the type host in the northwestern Mediterranean and a re-examination of the holotype. Scanning electron microscopy reveals ultrastructural details for the first time. The species is characterized by bothridia lined with gongylate columnar spinitriches and acicular filitriches on distal surfaces and with trullate spinitriches interspersed with acicular filitriches on proximal surfaces, in addition to a strobila covered in capilliform filitriches. This study also provides insights on diversity patterns of phyllobothriidean tapeworms across environmental gradients, enhances our understanding of the evolutionary relationships within the Phyllobothriidea, and provides information for future taxonomic and ecological studies.