Facelina annulicornis

Facelina annulicornis is an aeolid nudibranch that can be identified by its slender, elongated body and distinctive cerata, which are often brightly colored. This species is typically found in subtropical waters, ranging from County Donegal in Ireland down to Portugal and the Mediterranean Sea. It inhabits benthic environments, often residing at depths shallower than 40 meters, with the majority of sightings occurring at depths around 30 meters or less. As a predator, Facelina annulicornis primarily feeds on hydroids, particularly Halecium halecium, and may also consume other hydroids and possibly other aeolid nudibranchs. This species exhibits interesting reproductive behavior, as nudibranchs are simultaneous hermaphrodites. During mating, two individuals will engage in a unique courtship where they attempt to induce one another to act as male or female, with the dominant individual penetrating the body wall of the other. Diving encounters with Facelina annulicornis can be intriguing, as divers may observe them slowly moving across the substrate in search of prey. Their cryptic coloration may make them somewhat challenging to spot, but their presence adds to the biodiversity of the underwater environment. The conservation status of this species has not been evaluated by the IUCN, leaving its population status uncertain.