The identification and classification of flabelligerid polychaetes have been problematic due to three reasons: 1) the anterior end is rarely exposed and it carries the branchiae, whose type and arrangement are diagnostic; 2) there is no standardisation for naming chaetae; and 3) morphological delineations for most genera have been unstable. A redefinition and a revision of the type material of many species originally described in other genera but belonging to Trophoniella Hartman, 1959 are herein presented. Trophoniella together with Piromis Kinberg, 1856 and Pycnoderma Grube, 1877 share a very thick tunic and a projected branchial membrane which resembles a tongue. Their main difference is the type of neurochaetae in median and posterior chaetigers; thus, Trophoniella is redefined and restricted to include only the species with anchylosed hooks, whereas they are multiarticulated in Piromis and oligoarticulated in Pycnoderma; these two latter genera have been revised elsewhere. Therochaetella Hartman, 1967 is being regarded as a junior synonym of Trophoniella. The species of Trophoniella are further separated in two groups by the start of the anchylosed neurohooks (from about the chaetiger 10 or from median or posterior chaetigers). The species within each group can be separated by using the variation in the sediment cover and other attributes of noto- and neurochaetae. The genus as herein redefined contains, besides the type species, T. avicularia Caullery, 1944 from Indonesia, 26 species including 11 previously undescribed: T. americana (Monro, 1928) n. comb. from Galápagos and Panama, T. bastidai n. sp. from western Mexico, T. borealis (Hartman, 1965) n. comb. from northeastern South America, T. capitata (Nonato, 1966) n. comb. from Brazil, T. chilensis (Hartman, 1967) n. comb. from Chile, T. ehlersi (Day, 1973) n. comb. from the eastern United States, T. eliasi n. sp. from central Argentina, T. enigmatica n. sp. from the Mediterranean Sea, T. fauveli n. sp. from the Mediterranean Egyptian coast, T. fernandensis (Augener, 1918) reinstated, n. comb. from northwestern Africa, T. fiegei n. sp. from the Persian Gulf, T. grandis (Blanchard in Gay, 1849) n. comb. from central Chile, T. harrisae n. sp. from southern California, T. havaica (Kinberg, 1867) n. comb. from Hawaii, T. hospita (Fauchald, 1972) n. comb. from the Gulf of California, T. incerta (Augener, 1918) n. comb. from West Africa, T. indica (Fauvel, 1928) n. comb. from the Bay of Bengal, T. jareckiorum n. sp. from the Caribbean Sea, T. lindae n. sp. from the Caribbean Sea, T. minuta (Blanchard in Gay, 1849) n. comb. from Chile, T. orensanzi n. sp. from Uruguay, T. reishi n. sp. from the Gulf of California, T. rigida (Caullery, 1944) n. comb. from Indonesia, T. rudis (Grube & Müller in Grube, 1877) n. comb. from southern Brazil, T. salazarae n. sp. from western Mexico, and T. tumbensis (Hartmann-Schröder, 1962) n. comb. from Chile. Members of the species are marine and mainly tropical or subtropical, thriving in shallow bottoms.
Semiodera, Trophoniella, dorsal shield, sediment cover, anchylosed neurochaetae, new combinations, new species.