- Callinera
- Callinera Bergendal, 1900
- Calonemertes
- Calonemertes Coe, 1945
- Campbellonemertes Moore & Gibson, 1972
- Carcinonemertes
- Carcinonemertes Coe, 1902
- Carcinonemertidae
- Carcinonemertidae Coe, 1902
- Carinella
- Carinesta
- Carinesta Punnett, 1900
- Carinina
- Carinina Hubrecht, 1885
- Carinoma
- Carinoma Oudemans, 1885
- Carinomella
- Carinomella Coe, 1905
- Carinomidae
- Carinomidae
- Cephalomastax
- Cephalomastax Iwata, 1957
- Cephalothricidae
- Cephalothrix
- Cephalotrichidae McIntosh, 1874
- Cephalurichus
- Cephalurichus Gibson, 1985
- Cerebratula Van Beneden, 1861
- Cerebratulides
- Cerebratulides Stiasny-Wijnhoff, 1942
- Cerebratulina
- Cerebratulina Gibson, 1990
- Cerebratulus
- Cerebratulus Renier, 1804
- Chilineus
- Chilineus Friedrich, 1970
- Chunianna
- Chunianna Coe, 1954
- Chuniella
- Chuniella Brinkmann, 1917
- Chuniellidae
- Chuniellidae
- Coellidae
- Coenemertes
- Coenemertes
- Colemaniella
- Colemaniella Gibson, 1982
- Collarenemertes Chernyshev, 1993
- Communoporus
- Communoporus Friedrich, 1955
- Correanemertes
- Correanemertes
- Corsoua
- Corsoua Corrêa, 1963
- Crassonemertes
- Crassonemertes Brinkmann, 1917
- Cratenemertea
- Cratenemertes
- Cratenemertes Friedrich, 1955
- Cratenemertidae
- Cratenemertidae Friedrich, 1968
- Craticulineus
- Craticulineus Gibson, 1984
- Crybelonemertes
- Crybelonemertes Sundberg & Gibson, 1995
- Cryptonemertes
- Cryptonemertes Gibson, 1986
- Cuneonemertes
- Cuneonemertes Coe, 1926
- Curranemertes
- Curranemertes Kirsteuer, 1973
- Cyanonemertes Iwata, 2007
- Cyanophthalma
- Cyanophthalma Norenburg, 1986