• Abyssoninoe abyssorum (McIntosh, 1885)
• Abyssoninoe bidentata D'Alessandro, Cosentino, Giacobbe, Andaloro & Romeo, 2014
• Abyssoninoe galatheae (Knox & Green, 1972)
• Abyssoninoe hibernica (McIntosh, 1903)
• Abyssoninoe orensanzi Hartmann-Schröder & Rosenfeldt, 1992
• Abyssoninoe phuketensis Oug, 2002
• Abyssoninoe scopa (Fauchald, 1974)
• Abyssoninoe scopa aequilobata (Winsnes, 1981) accepted as Abyssoninoe hibernica (McIntosh, 1903)
• Abyssoninoe winsnesae Frame, 1992
• Aciculomarphysa comes Hartmann-Schröder in Hartmann-Schröder & Zibrowius, 1998
• Albertaprion comis (Eller, 1938) †
• Albertaprion demisiccius Jansonius & Craig, 1974 †
• Americonuphis magna (Andrews, 1891)
• Americonuphis reesei Fauchald, 1973
• Anchidorvillea moniliformis Hilbig & Blake, 1991
• Anchinothria cirrobranchiata (Moore, 1903)
• Anchinothria cobra (Chamberlin, 1919)
• Anchinothria crassisetosa (Chamberlin, 1919)
• Anchinothria fissurata (Fauchald, 1972)
• Anchinothria glutinatrix (Ehlers, 1887)
• Anchinothria hiatidentata (Moore, 1911)
• Anchinothria macrobranchiata (McIntosh, 1885)
• Anchinothria parvula Budaeva & Paxton, 2013
• Anchinothria pettiboneae Budaeva & Paxton in Kupriyanova et al. 2026
• Anchinothria pourtalesii (Ehlers, 1879)
• Anchinothria pycnobranchiata (McIntosh, 1885)
• Anchinothria sombreriana (McIntosh, 1885)
• Anchinothria tosaensis Imajima, 1999
• Andiprion paxtonae Hints, Tonarová, Eriksson, Rubinstein & De la Puente, 2017 †
• Apodotrocha progenerans Westheide & Riser, 1983
• Apodotrocha tobik Koroleva & Tzetlin in Koroleva et al., 2026
• Aponuphis annae Paxton, 2017
• Aponuphis bellani Paxton, 2017
• Aponuphis bilineata (Baird, 1870)
• Aponuphis bilineata grubii (Marenzeller, 1886) accepted as Aponuphis grubii (Marenzeller, 1886)
• Aponuphis brementi (Fauvel, 1916)
• Aponuphis chistikovi Detinova, 1986
• Aponuphis danicae Paxton, 2017
• Aponuphis fauveli (Rioja, 1918) accepted as Aponuphis brementi (Fauvel, 1916)
• Aponuphis grubii (Marenzeller, 1886)
• Aponuphis ornata (Fauvel, 1928)
• Aponuphis rigida (Claparède, 1868)
• Aponuphis willsiei Cantone & Bellan, 1996
• Aponuphis willsii [auct.] accepted as Aponuphis willsiei Cantone & Bellan, 1996
• Apophryotrocha mutabiliseta Jumars, 1974 (uncertain > taxon inquirendum)
• Arabella (Arabella) iricolor (Montagu, 1804) accepted as Arabella iricolor (Montagu, 1804)
• Arabella (Arabella) pulvinata Zanol & Ruta, 2015
• Arabella (Cenothrix) mutans (Chamberlin, 1919)
• Arabella (Cenothrix) robusta Zanol & Ruta, 2015
• Arabella ampulliformis Darbyshire & Kara, 2024
• Arabella aracaensis Steiner & Amaral, 2009
• Arabella atlantica Crossland, 1924
• Arabella cincta Hartmann-Schröder, 1962
• Arabella coeca Fauvel, 1940
• Arabella debilis (Ehlers, 1887) accepted as Drilonereis debilis (Ehlers, 1887)
• Arabella diversimaxillata Szaniawski & Gaździcki, 1978 †
• Arabella endonata Emerson, 1974
• Arabella geniculata (Claparède, 1868)
• Arabella geniculata japonica Okuda, 1939
• Arabella gouqi Anton, Mohamedi & Yongjiu 2026
• Arabella iricolor (Montagu, 1804)
• Arabella iricolor caerulea (Schmarda, 1861)
• Arabella iricolor iricolor (Montagu, 1804)
• Arabella iridescens Treadwell, 1906
• Arabella logani Crossland, 1924
• Arabella longicirrata Hartmann-Schröder, 1979 accepted as Arabella iricolor (Montagu, 1804)
• Arabella longipedata Monro, 1931
• Arabella maculifera (Grube, 1878)
• Arabella mimetica Chamberlin, 1919
• Arabella monroi Colbath, 1989
• Arabella multidentata (Ehlers, 1887)
• Arabella mutans (Chamberlin, 1919)
• Arabella nesidensis (Delle Chiaje, 1828)
• Arabella novecrinita Crossland, 1924
• Arabella panamensis Colbath, 1989
• Arabella pectinata Fauchald, 1970
• Arabella protomutans Orensanz, 1990
• Arabella renierii (Grube, 1877)
• Arabella rolandi (Delle Chiaje, 1828)
• Arabella semimaculata (Moore, 1911)
• Arabella turbidiricolor Kang, Jeong, Choi & Yoon, 2024
• Arabella umgazanae Darbyshire & Kara, 2024
• Arabella zonata (Moore, 1903)
• Arabelloneris broomensis Hartmann-Schröder, 1979
• Arabelloneris janeirensis (Augener, 1934)
• Arenotrocha lanzarotensis Brito & Núñez, 2003
• Arenotrocha minuta (Lévi, 1954)
• Arites eocaenicus Rákosi, 1981 †
• Arites keuperianus Kozur, 1967 †
• Arites minor Rákosi, 1981 †
• Arites sibiricus Zaslavskaya, 1989 †
• Arites vulgaris Kozur, 1967 †
• Atraktoprion anatinus (Stauffer, 1939) †
• Atraktoprion cornutus Kielan-Jaworowska, 1962 †
• Atraktoprion eudoxus Szaniawski, 1968 †
• Atraktoprion major Kielan-Jaworowska, 1966 †
• Atraktoprion mirabilis Kielan-Jaworowska, 1966 †
• Atraktoprion podolicus Szaniawski & Drygant, 2014 †
• Atraktoprion robustus Kielan-Jaworowska, 1966 †
• Augeneria albidentata (Ehlers, 1908)