Acanthobothrium oualimeriemae n. sp. (Eucestoda: Onchobothriidae) from the spiral valve of the skates Raja asterias...

A new species of Acanthobothrium is described from the spiral intestine of Raja asterias Delaroche and Raja radula Delaroche in the Algerian Mediterranean Sea. Acanthobothrium oualimeriemae n. sp. was characterized using an integrative approach combining morphological and molecular (28S rDNA) data. The new species is assigned to morphological category 2 and can be distinguished from all known congeners by a unique combination of features, including total body length, number of proglottids, scolex configuration, dimensions of bothridial structures, length of the cephalic peduncle, length of the cirrus pouch, and number of testes. Overall, our phylogenetic analyses revealed that all three Mediterranean nominal Acanthobothrium species, for which 28S rDNA sequences are available clustered, within the same clade, indicating a close evolutionary affinity particularly with A. minus Tazerouti, Kechemir-Issad & Euzet, 2009 (Category 2 species) and A. coronatum (Rudolphi, 1819) Blanchard, 1848 (Category 4 species). The close affinity between A. oualimeriemae n. sp. and A. minus may be related to their shared Mediterranean distribution and morphological similarity, although the limited resolution of 28S rDNA warrants cautious interpretation. These findings support the view that, although these taxonomic categories are useful for morphological comparisons, they are not congruent with actual phylogenetic relationships. Furthermore, our results suggest that the commonly used 28S rDNA region in molecular systematics of cestodes infecting elasmobranchs is generally effective for resolving higher-level phylogenetic relationships, confirming the validity of established genera. However, our findings also indicate that this molecular marker does not always provide sufficient resolution to distinguish closely related species. This limitation is evident within the genus Acanthobothrium, where morphologically distinct species may remain poorly resolved based on 28S rDNA data alone.