A morphological and molecular characterisation of Tristoma integrum Diesing, 1850 (Monogenea, Capsalidae) including its complete mitogenome

Capsalids are monopisthocotylean monogeneans parasites on the skin and gills of fish. Capsalines (subfamily Capsalinae) are large-sized capsalids parasitic on highly-prized gamefish, and species of Tristoma parasitize only the gills of swordfish (Xiphias gladius). We obtained specimens of Tristoma integrum Diesing, 1850 from swordfish collected off Algeria in the Mediterranean Sea. We describe the specimens, including the key systematics characters of dorsolateral body sclerites. One specimen was used for a New Generation Sequencing analysis but a part of it, including the sclerites, was mounted on a permanent slide, drawn, and deposited in a curated collection for future record. We characterised the complete mitogenome, the ribosomal cluster (including 18S and 28S) and additional genes such as EF1a elongation factor 1 alpha and Histone 3. We also retrieved molecular information from the host tissue present in the gut of the monogenean and provide the cox1 sequence of the host, X. gladius. The mitogenome of T. integrum is 13,968 bp in length and codes for 12 protein genes, 2 rRNA and 22 tRNA. Phylogenies of capsalids were generated from 28S sequences and concatenated mitochondrial protein-coding genes, respectively. In the 28S phylogeny, most subfamilies based on morphology were not found monophyletic, but the Capsalinae were monophyletic. In both phylogenies, the closest members to Tristoma spp. was a member of Capsaloides. In an Appendix, we report the complex nomenclatural history of Tristoma and its species.