First report of adults of Acanthocephaloides irregularis from cuttlefish Sepia officinalis (Cephalopoda) in Tunisia: SEM observations and molecular analysis.

Abstract

During a parasitological survey of the common cuttlefish Sepia officinalis (Linnaeus) collected from the Bizerte Lagoon in northern Tunisia, adult acanthocephalans were found attached to the internal wall of cuttlefish stomach. The presence of adult acanthocephalans in cephalopods is unusual, given that definitive hosts for these obligate endoparasites are typically vertebrates. A detailed morphological examination of both sexes using light and scanning electron microscopy revealed high morphological similarities to Acanthocephaloides irregularis Amin, Oğuz, Heckmann, Tepe et Kvach, 2011. A partial sequence of 604 bp of the cytochrome oxidase subunit I (COI) gene was successfully generated. Phylogenetic analysis based on COI gene confirmed the identification, showing that the Tunisian isolate of A. irregularis clustered closely to A. propinquus (Dujardin, 1845) from Gobius bucchichii Steindachner. This study presents the first record of A. irregularis in S. officinalis in the Mediterranean Sea, offering new insights into its life cycle, host specificity, and ecological significance within benthic food webs. This finding raises important questions about the role of cephalopod hosts in the transmission dynamics of acanthocephalans in marine environments.