• Aaptotoichus challengeri Holbourn & Kaminski, 1995 †: meiobenthos
• Aaptotoichus clavellatus (Loeblich & Tappan, 1946) †: meiobenthos
• Aaptotoichus mutinensis Haig & McCartain, 2010 †: meiobenthos
• Aaptotoichus quinnaniensis Haig, 2003 †: meiobenthos
• Aaptotoichus vallis (Trifonova, 1967) †: meiobenthos
• Abadehella biconvexa Okimura & Ishii, 1975 †: meiobenthos
• Abadehella coniformis Okimura & Ishii, 1975 †: meiobenthos
• Abadehella grandis Pronina-Nestell, 2001 †: meiobenthos
• Abadehella iwaiensis Kobayashi, 1997 †: meiobenthos
• Abadehella koryakiensis Daydov in Davydov et al., 1996 †: meiobenthos
• Abadehella mengcunensis Wang, 2002 †: meiobenthos
• Abadehella minima Wang in Zhao et al., 1981 †: meiobenthos
• Abadehella tarazi Okimura & Ishii, 1975 †: meiobenthos
• Abadehellopsis longlinensis (Lin, Li & Sun, 1990) †: meiobenthos
• Abadehellopsis pauciseptata Vachard in Krainer, Vachard & Schaffhauser, 2019 †: meiobenthos
• Abadehellopsis protea (Cushman & Waters, 1928) †: meiobenthos
• Abadehellopsis regularis (Lin, Li & Sun, 1990) †: meiobenthos
• Abadehellopsis regularisaeformis (Lin, Li & Sun, 1990) †: meiobenthos
• Abditodentrix pseudothalmanni (Boltovskoy & Guissani de Kahn, 1981): meiobenthos
• Abdullaevia tosbulakensis Suleymanov, 1965 †: meiobenthos
• Abelbolla boucheri Huang & Zhang, 2004: meiobenthos
• Abelbolla huanghaiensis Huang & Zhang, 2004: meiobenthos
• Abelbolla maemulensis Hong & Lee, 2014: meiobenthos
• Abelbolla major Hiang, Wang & Huang, 2015: meiobenthos
• Abelbolla warwicki Huang & Zhang, 2004: meiobenthos
• Aberisphaera gambanica Wan, 1991 †: meiobenthos
• Abnitocrella eberhardi Karanovic, 2006: meiobenthos
• Abnitocrella halsei Karanovic, 2006: meiobenthos
• Abnitocrella newmanensis Karanovic, 2006: meiobenthos
• Aborjinia eulagiscae (Tchesunov & Spiridonov, 1985) Özdikmen, 2010: meiobenthos
• Aborjinia profunda Zograf, Semenchenko & Mordukhovich, 2024: meiobenthos
• Abrardia catalaunica Bilotte, 1974 †: meiobenthos
• Abrardia mosae (Hofker, 1955) †: meiobenthos
• Abriolina mediterranea Luperto, 1964 †: meiobenthos
• Abscondicola humesi Fiers, 1990: meiobenthos
• Abuhammadina saidi Abd-Elshafy & Ibrahim, 1990 †: meiobenthos
• Abyssalia foliformis Gooday & Holzmann, 2020: meiobenthos
• Abyssalia sphaerica Gooday & Holzmann, 2020: meiobenthos
• Abyssamina incisa Schnitker & Tjalsma, 1980 †: meiobenthos
• Abyssamina poagi Schnitker & Tjalsma, 1980 †: meiobenthos
• Abyssamina quadrata Schnitker & Tjalsma, 1980 †: meiobenthos
• Abyssotherma pacifica Brönnimann, Van Dover & Whittaker, 1989: meiobenthos
• Acanthodasys aculeatus Remane, 1927: meiobenthos
• Acanthodasys algarvense Hummon, 2008: meiobenthos
• Acanthodasys arcassonensis Kisielewski, 1987: meiobenthos
• Acanthodasys australis Bosco, Lourenço, Guidi, Balsamo, Hochberg & Garraffoni, 2020: meiobenthos
• Acanthodasys caribbeanensis Hochberg & Atherton, 2010: meiobenthos
• Acanthodasys carolinensis Hummon, 2008: meiobenthos
• Acanthodasys comtus Lee, 2012: meiobenthos
• Acanthodasys ericinus Lee, 2012: meiobenthos
• Acanthodasys fibrosus Clausen, 2004: meiobenthos
• Acanthodasys flabellicaudus Hummon & Todaro, 2009: meiobenthos
• Acanthodasys lineatus Clausen, 2000: meiobenthos
• Acanthodasys paurocactus Atherton & Hochberg, 2012: meiobenthos
• Acanthodasys silvulus Evans, 1992: meiobenthos
• Acanthohalacarus reticulatus Bartsch, 2001: meiobenthos
• Acantholaimus aheneus Bussau, 1993: meiobenthos
• Acantholaimus akvavitus Gerlach, Schrage & Riemann, 1979: meiobenthos
• Acantholaimus angustus Bussau, 1993: meiobenthos
• Acantholaimus arminius Gerlach, Schrage & Riemann, 1979: meiobenthos
• Acantholaimus arthrochaeta Miljutina & Miljutin, 2012: meiobenthos
• Acantholaimus barbatus Miljutina & Miljutin, 2012: meiobenthos
• Acantholaimus bidentatus Manoel, Esteves & Neres, 2022: meiobenthos
• Acantholaimus caecus Bussau, 1993: meiobenthos
• Acantholaimus calathus Gerlach, Schrage & Riemann, 1979: meiobenthos
• Acantholaimus cornutus Miljutina & Miljutin, 2012: meiobenthos
• Acantholaimus coruscus Bussau, 1993: meiobenthos
• Acantholaimus cyathibucca Vivier, 1985: meiobenthos
• Acantholaimus elegans Jensen, 1988: meiobenthos
• Acantholaimus formosus Miljutina, Miljutin & Tchesunov, 2013: meiobenthos
• Acantholaimus gathumai Muthumbi & Vincx, 1997: meiobenthos
• Acantholaimus geraerti Muthumbi & Vincx, 1997: meiobenthos
• Acantholaimus gigantasetosus Vivier, 1985: meiobenthos
• Acantholaimus heipi Muthumbi & Vincx, 1997: meiobenthos
• Acantholaimus incomptus Vivier, 1985: meiobenthos
• Acantholaimus invaginatum Muthumbi & Vincx, 1997: meiobenthos
• Acantholaimus iubilus Gerlach, Schrage & Riemann, 1979: meiobenthos
• Acantholaimus longisetosus Allgén, 1933: meiobenthos
• Acantholaimus longistriatus Gourbault & Vincx, 1985: meiobenthos
• Acantholaimus macramphis Gourbault & Vincx, 1985: meiobenthos
• Acantholaimus maks Gerlach, Schrage & Riemann, 1979: meiobenthos
• Acantholaimus marliae Manoel, Silva & Esteves, 2017: meiobenthos
• Acantholaimus megamphis Vivier, 1985: meiobenthos
• Acantholaimus microdontus Gourbault & Vincx, 1985: meiobenthos
• Acantholaimus minutus (Vitiello, 1972) Gerlach, Schrage & Riemann, 1979: meiobenthos
• Acantholaimus obviatus Vivier, 1985: meiobenthos
• Acantholaimus occultus Bussau, 1993: meiobenthos
• Acantholaimus polydentatus Gerlach, 1951: meiobenthos
• Acantholaimus pugious Manoel, Esteves & Neres, 2022: meiobenthos
• Acantholaimus quadridentatus Jensen, 1985: meiobenthos
• Acantholaimus quintus Gerlach, Schrage & Riemann, 1979: meiobenthos
• Acantholaimus robustus Miljutina & Miljutin, 2012: meiobenthos
• Acantholaimus septimus Gerlach, Schrage & Riemann, 1979: meiobenthos
• Acantholaimus setosus Vitiello, 1970: meiobenthos
• Acantholaimus sieglerae Miljutina & Miljutin, 2012: meiobenthos
• Acantholaimus skukinae Miljutina, Miljutin & Tchesunov, 2013: meiobenthos
• Acantholaimus spinicauda (Vitiello, 1970) Gerlach, Schrage & Riemann, 1979: meiobenthos
• Acantholaimus tchesunovi Miljutina & Miljutin, 2012: meiobenthos
• Acantholaimus tectus Bussau, 1993: meiobenthos
• Acantholaimus veitkoehlerae Miljutina & Miljutin, 2012: meiobenthos