First Record of Urceolaria carmenae n. sp. (Ciliophora, Peritrichia, Mobilida) Infesting the Gills of Octopus bimaculatus Verrill from the Gulf of California, Mexico

Ciliate infestations in aquatic organisms are commonly associated with aquaculture, yet their impact on natural ecosystems remains largely understudied. This study describes a mobilid peritrich species infesting the gills of Octopus bimaculatus from the Gulf of California, Mexico. All 76 examined hosts (100%) exhibited infestation, with a mean intensity of 687 ± 228 (279–1077) urceolariid cells per gill. The ciliate cells displayed morphological traits consistent with those of the genus Urceolaria: turban-shaped cells measuring 44.2 ± 13.2 (31.3–88.6) µm in diameter; an adhesive disc of 36.5 ± 10.7 (29.2–74.6) μm in diameter; 18–19 plates measuring 11.0 ± 0.86 (9–12) µm in length; and 166–169 radial pins. Phylogenetic analysis of 18S rDNA sequences placed this species within the genus Urceolaria, a sister group to Urceolaria urechi and Urceolaria serpularum, with a genetic distance of 1.0% with respect to the previously described species. Combined morphological and molecular data support the description of a new species, Urceolaria carmenae n. sp. This is the first record of a mobilid peritrich in cephalopod mollusks, thereby enhancing our understanding of the diversity of ciliates among marine invertebrates in their natural habitats.