|aktə(ˌ)nōˈtrikēəm noun
also ac·tin·o·trich akˈtinəˌtrik
( plural ac·ti·no·trich·ia -ˈtrikēə ; also ac·tin·o·trichs -ˌtriks)
Etymology: New Latin actinotrichium, from actin- + Greek trich-, thrix hair + New Latin -ium — more at trich-
: any of the hairy threadlike fibers in the fin fold of an embryo fish which fuse and form the base of the rays