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Fionidae Family

Family Fionidae

Up until December of 2016 the family Fionidae contained just a single species, the globally distributed Fiona pinnata. Since the publishing of new molecular phylogeny research, combined with the taxonomic rules of precedence, it is now the largest of the aeolid families taking on board the members of the Tergipedidae, Eubranchidae and Calmidae families. Fionidae is a family of mostly small species, although a few may be longer than 50 mm crawling length. They have an elongate body that tapers posteriorly, but that shape may often be disguised by the profusion of cerata on the dorsum. The foot is often wider than the body. The anterior corners are usually rounded, but they can be tentacular in some species (propodial tentacles). The oral tentacles are smooth and can range in length from short to long in relation to rhinophore length. The rhinophores are long and usually smooth, but they can be wrinkled in some species. There is often a distinct pericardial swelling on the dorsum immediately behind the rhinophores. The cerata are tubular or sometimes fusiform and smooth for the most part, but in some species they appear pleated. The cerata are arranged obliquely down each side of the body and are sometimes positioned upon ridges. In Eubranchus though the cerata are characteristically swollen or inflated in appearance sometimes bearing tubercular swellings and showing a central constriction, or a sub-terminal swelling and are comparatively few in number being arranged in simple rows down each side of the body. In Fiona the cerata possess a characteristic undulating membrane down their inner margin, but do not contain cnidosacs. Most Fionidae feed upon hydroids, however those members previously known as Phestilla feed upon the hard (scleractinian) corals such as Porites and Tubastraea, and possibly because the nematocysts of these hard corals are unsuitable to use for defence for some reason, there is a swollen glandular region at the tip of the cerata in place of a cnidosac. Fiona pinnata feeds on goose barnacles (Lepas spp.) which are attached to floating material, or directly on the floating colonial hydroids Physalia and Velella. Note: The genera Trinchesia, Cuthona (except Cuthona nana), Phestilla and Catriona are synonymized with (replaced by) the genus Tenellia.