Re-description and molecular characterization of Acanthobothrium minus Tazerouti, Kechemir-Issad, and Euzet, 2009 (Onchoproteocephalidea, Onchobothriidae) from two skates (Elasmobranchii, Rajidae) off the Algerian Coast, Western Mediterranean

Abstract Acanthobothrium represents the most species-rich genus of onchoproteocephalidean cestodes, with adults parasitizing the spiral valves of elasmobranch fishes. Between October 2023 and August 2025, Acanthobothrium minus , previously reported from the Algerian coast in Raja asterias (Mediterranean starry ray), was collected from the spiral valve of Raja asterias , and the rough ray, Raja radula . This parasite is characterized by its small body size and reduced number of proglottids. In this study, we examine its host specificity and provide a redescription of A. minus from the type locality and host, and an additional host ( R. radula ) using light microscopy and molecular approaches. Furthermore, we present, for the first time, molecular and phylogenetic data based on 28S rDNA sequences for this species, along with a detailed morphometric comparison to other CategoryII Acanthobothrium species infecting Rajidae from the Mediterranean. Our phylogenetic results show all Acanthobothrium species 28S sequences from the Mediterannean grouping in the same clade and suggest close affinity with Acanthobothrium coronatum (Category 4). These results support that these taxonomic categories are a useful guide for morphological comparisons but are not correlated with true phylogenetic relationships. Furthermore, the regional grouping of these sequences from relatively distantly related definitive hosts (the shark Scyliorhinus stellaris L. and the skates R. asterias and R. radula ) supports evolution of this elasmobranch- Acanthobothrium association in the Mediterranean through host switching due to shared ecological features of the hosts followed by speciation by isolation. However, additional support for this hypothesis would require more in-depth taxonomic representation of available sequence data.