Ac
- Achoronemertes Crandall & Gibson, 1998
- Acrostomum Oersted, 1843
- Acteonemertes Pantin, 1961
- Acteonemertidae Chernyshev, 2005
Ad
- Adenorhagas Riser, 1990
Ae
- Aegialonemertes Gibson, 1990
Aenigmanemertes Sundberg & Gibson, 1995
- Aenigmanemertes norenburgi Sundberg & Gibson, 1995 [1]
Nemertea → Enopla → Monostilifera → Eumonostilifera → Emplectonematidae
- Aetheolineus Senz, 1993
- Aetheorhynchus Gibson, 1981
Af
- Africanemertes Stiasny-Wijnhoff, 1942
Al
- Alaonemertes Stiasny-Wijnhoff, 1942
Alaxinus Gibson Wickham & Kuris, 1990
- Alaxinus oclairi Gibson, Wickham & Kuris, 1990
Nemertea → Enopla → Monostilifera → Eumonostilifera → Amphiporidae
- Albanemertes Senz, 1993
- Alexandronemertes Tshernyshev, 1992
- Algonemertes Corrêa, 1954
Am
- Ammolineus Senz, 2001
- Ammonemertes Gibson, 1990
- Amniclineus Gibson & Qi, 1991
- Amorphonemertes Cantell, 1998
- Amphinemertes Coe, 1940
- Amphiporella
- Amphiporidae
- Amphiporus Ehrenberg, 1831
An
- Annulonemertes Berg, 1985
- Anopla
- Antarctolineus Muller & Scripcariu, 1964
- Antarctonemertes Friedrich, 1955
- Antiponemertes Moore & Gibson, 1981
Ap
- Apatronemertes Wilfert & Gibson, 1974
Ar
- Arctonemertes Friedrich, 1957
- Arenonemertes Friedrich, 1933
- Argonemertes Moore & Gibson, 1981
- Arhynchonemertes
- Arhynchonemertidae Chernyshev, 1995
- Armaueria Brinkmann, 1932
- Armaueriidae
As
- Ascaris Linnaeus, 1758
- Astemma Örsted, 1843
- Asteronemertes Tshernyshev in Chernyshev, 1991
At
- Atrionemertes Senz, 1993
- Atyponemertes Friedrich, 1938
Au
- Australineus Gibson, 1990
- Austroprostoma Stiasny-Wijnhoff, 1942