Revision of Stylarioides delle Chiaje, 1831 (Annelida: Flabelligeridae)

There has been confusion regarding the delineation of genera in the Flabelligeridae. Thus, it is not surprising that some genera like Pherusa Oken, 1807 currently include different body patterns with differing branchial and chaetal features. A revision of all materials available has allowed a standardized approach; one of its results has been the restriction of Pherusa to encompass species provided with eight branchial filaments and anchylosed neurochaetae. At the same time, Stylarioides delle Chiaje, 1831, with Stylarioides monilifer delle Chiaje, 1831, as its type species, which has been wrongly regarded as a junior synonym of other flabelligerid genera, is reinstated, restricted and revised. It includes species whose members have cylindrical bodies, often tapering into a distinct, thinner cauda, and their tunic includes a variable amount of sediment grains on their papillae. The branchiae are arranged in two lateral spirals, often transformed into a serpuloid branchia by having two lateral branchial peduncles, each with filaments arranged in spiral; the body papillae are short, and their chaetae include fine, short, multiarticulate notochaetae, and short, anchylosed neurohooks. Coppingeria Haswell, 1892, a monotypic genus defined by the presence of two branchial peduncles with spiral filaments, is regarded as a junior synonym of Stylarioides. The species included are S. monilifer from the Mediterranean Sea, S. bengalensis Fauvel, 1932, from India, S. granulosus Caullery, 1944, from the Java Sea, S. grubei n. sp. from the Red Sea, S. hirsutus Lo Bianco, 1893, from the Mediterranean Sea, S. longisetosa (Haswell, 1892) n. comb., from Australia, S. muiri n. sp. from Tristan da Cunha, S. plantei n. sp. from Madagascar, S. saldanha (Day, 1961) n. comb., from South Africa, S. swakopianus Augener, 1918, from Western Africa, and S. tropicus Augener, 1918, from Western Africa. Other species provided with lateral pedunculate branchiae differ from Stylarioides by having a racket-shaped peduncle, where the thin branchial filaments are separated into two lateral groups, each with filaments arranged in parallel lines. Further, their body has a truncate posterior end, larger cephalic cage chaetae, and larger notochaetae and neurohooks. For these species, Treadwellius n. gen. is proposed, with Stylarioides atentacula Hoagland, 1920, as the type species. The species included are T. atentacula (Hoagland, 1920) n. comb, from the Philippine Islands, T. bifidus (Fauvel, 1932), from the Arabian Sea, and T. gilleti n. sp. from Western Africa.