• Abacella pertusa Maslov
• Acanthocodium fragile Suringar, 1867 accepted as Codium fragile (Suringar) Hariot, 1889
• Acanthosphaera tenuispina Korshikov, 1953 accepted as Acanthosphaera zachariasii Lemmermann, 1899
• Acanthosphaera zachariasii Lemmermann, 1899
• Acetabularia acetabulum (Linnaeus) P.C.Silva, 1952
• Acetabularia antillana (Solms-Laubach) Egerod, 1952 accepted as Chalmasia antillana Solms-Laubach, 1895
• Acetabularia calyculus J.V.Lamouroux, 1824
• Acetabularia caraibica Kützing, 1856 accepted as Acetabularia crenulata J.V.Lamouroux, 1816 represented as Acetabularia subg. Acicularia crenulata J.V. Lamouroux, 1816
• Acetabularia caribaeum Lamarck, 1816 accepted as Acetabularia crenulata J.V.Lamouroux, 1816 represented as Acetabularia subg. Acicularia crenulata J.V. Lamouroux, 1816
• Acetabularia clavata Yamada, 1934 accepted as Parvocaulis clavatus (Yamada) S.Berger, U.Fettweiss, S.Gleissberg, L.B.Liddle, U.Richter, H.Sawitzky & G.C.Zuccarello, 2003
• Acetabularia crenulata J.V.Lamouroux, 1816 represented as Acetabularia subg. Acicularia crenulata J.V. Lamouroux, 1816
• Acetabularia crenulata var. major Sonder, 1871 accepted as Acetabularia major G.Martens, 1866
• Acetabularia dentata Solms-Laubach, 1895
• Acetabularia denudata Zanardini, 1878 accepted as Acetabularia major G.Martens, 1866
• Acetabularia exigua Solms-Laubach, 1895 accepted as Parvocaulis polyphysoides (P.Crouan & H.Crouan) S.Berger, U.Fettweiss, S.Gleissberg, L.B.Liddle, U.Richter, H.Sawitzky & G.C.Zuccarello, 2003
• Acetabularia farlowii Solms-Laubach, 1895 represented as Acetabularia subg. Acicularia farlowii Solms-Laubach, 1895
• Acetabularia gigas Solms-Laubach, 1895 accepted as Acetabularia major G.Martens, 1866
• Acetabularia haemmerlingii H.G.Schweiger & Berger, 1975
• Acetabularia integra J.V.Lamouroux accepted as Acetabularia acetabulum (Linnaeus) P.C.Silva, 1952
• Acetabularia kilneri J.Agardh, 1887
• Acetabularia major G.Martens, 1866
• Acetabularia mediterranea J.V.Lamouroux, 1816 accepted as Acetabularia acetabulum (Linnaeus) P.C.Silva, 1952
• Acetabularia minutissima Okamura, 1912 accepted as Parvocaulis parvulus (Solms-Laubach) S.Berger, Fettweiss, Gleissberg, Liddle, U.Richter, Sawitzky & Zuccarello, 2003
• Acetabularia miocenica Andrussow, 1887 † (uncertain)
• Acetabularia moebii Solms-Laubach, 1895 accepted as Parvocaulis parvulus (Solms-Laubach) S.Berger, Fettweiss, Gleissberg, Liddle, U.Richter, Sawitzky & Zuccarello, 2003
• Acetabularia myriospora A.B.Joly & Cordeiro-Marina, 1965
• Acetabularia parvula Solms-Laubach, 1895 accepted as Parvocaulis parvulus (Solms-Laubach) S.Berger, Fettweiss, Gleissberg, Liddle, U.Richter, Sawitzky & Zuccarello, 2003
• Acetabularia parvula var. americana W.R.Taylor, 1945 accepted as Parvocaulis parvulus (Solms-Laubach) S.Berger, Fettweiss, Gleissberg, Liddle, U.Richter, Sawitzky & Zuccarello, 2003
• Acetabularia peniculus (R.Brown ex Turner) Solms-Laubach, 1895
• Acetabularia peniculus var. cliftonii (Harvey) Solms-Laubach, 1895 accepted as Acetabularia peniculus (R.Brown ex Turner) Solms-Laubach, 1895
• Acetabularia philippinensis Gilbert, 1943 accepted as Acetabularia ryukyuensis Okamura & Yamada, 1932
• Acetabularia polyphysoides P.Crouan & H.Crouan, 1865 accepted as Parvocaulis polyphysoides (P.Crouan & H.Crouan) S.Berger, U.Fettweiss, S.Gleissberg, L.B.Liddle, U.Richter, H.Sawitzky & G.C.Zuccarello, 2003
• Acetabularia polyphysoides f. deltoidea (M.A.Howe) F.S.Collins, 1909 accepted as Polyphysa myriospora (A.B.Joly & Cordiero-Marinha) S.Berger & M.J.Kaever, 1992 accepted as Acetabularia myriospora A.B.Joly & Cordeiro-Marina, 1965
• Acetabularia pusilla (M.A.Howe) F.S.Collins, 1909 accepted as Parvocaulis pusillus (M.Howe) S.Berger, U.Fettweiss, S.Gleissberg, L.B.Liddle, U.Richter, H.Sawitzky & G.C.Zuccarello, 2003
• Acetabularia roxasii Troño, Santiago & Ganzon-Fortes, 1978 accepted as Acetabularia ryukyuensis Okamura & Yamada, 1932
• Acetabularia ryukyuensis Okamura & Yamada, 1932
• Acetabularia ryukyuensis var. philippinensis (Gilbert) Valet, 1943
• Acetabularia schenckii K.Möbius, 1889 represented as Acetabularia subg. Acicularia schenckii K. Möbius, 1889
• Acetabularia subg. Acetabularia acetabulum (Linnaeus) P.C.Silva, 1952 represented as Acetabularia acetabulum (Linnaeus) P.C.Silva, 1952
• Acetabularia subg. Acicularia caliculus J.V. Lamouroux, 1824 represented as Acetabularia calyculus J.V.Lamouroux, 1824
• Acetabularia subg. Acicularia crenulata J.V. Lamouroux, 1816
• Acetabularia subg. Acicularia crenulata var. monodisca Børgesen, 1936
• Acetabularia subg. Acicularia dentata Solms-Laubach, 1895
• Acetabularia subg. Acicularia farlowii Solms-Laubach, 1895
• Acetabularia subg. Acicularia kilneri J. Agardh represented as Acetabularia kilneri J.Agardh, 1887
• Acetabularia subg. Acicularia major G. Martens represented as Acetabularia major G.Martens, 1866
• Acetabularia subg. Acicularia ryukyuensis Okamura & Yamada, 1932 represented as Acetabularia ryukyuensis Okamura & Yamada, 1932
• Acetabularia subg. Acicularia ryukyuensis var. philippinensis (Gilbert) Valet, 1943 represented as Acetabularia ryukyuensis var. philippinensis (Gilbert) Valet, 1943
• Acetabularia subg. Acicularia schenckii K. Möbius, 1889
• Acetabularia suhrii Solms-Laubach, 1895 accepted as Acetabularia calyculus J.V.Lamouroux, 1824
• Acetabularia toxasii Troño, Santiago & Ganzon-Fortes, 1978
• Acetabularia tsengiana Egerod, 1952 accepted as Parvocaulis exiguus (Solms-Laubach) S.Berger, U.Fettweiss, S.Gleissberg, L.B.Liddle, U.Richter, H.Sawitzky & G.C.Zuccarello, 2003
• Acetabularia velasquezii Troño, Santiago & Ganzon-Fortes, 1978 accepted as Parvocaulis parvulus (Solms-Laubach) S.Berger, Fettweiss, Gleissberg, Liddle, U.Richter, Sawitzky & Zuccarello, 2003
• Acetabularia wettsteinii Schussnig, 1930 accepted as Parvocaulis parvulus (Solms-Laubach) S.Berger, Fettweiss, Gleissberg, Liddle, U.Richter, Sawitzky & Zuccarello, 2003
• Acicularia alaica Maslov (uncertain)
• Acicularia albrightii Johnson & Kaska
• Acicularia americana Konishi & Epis
• Acicularia andrussowi Solms-Laubach, 1895 † (uncertain)
• Acicularia antiqua Pia (uncertain)
• Acicularia archiaci L.Morellet & J.Morellet (uncertain)
• Acicularia clapei Jaffrezo
• Acicularia clavata L.Morellet & J.Morellet
• Acicularia comanchense Johnson
• Acicularia cornigera L.Morellet & J.Morellet, 1922 †
• Acicularia dyumatsenae Pia
• Acicularia endoi Praturlon (uncertain)
• Acicularia eocaenica Munier-Chalmas ex L.Morellet & J.Morellet
• Acicularia ferganensis Maslov
• Acicularia gracilis L.Morellet & J.Morellet (uncertain)
• Acicularia guatemalaica Johnson & Kaska (uncertain)
• Acicularia heberti L.Morellet & J.Morellet (uncertain)
• Acicularia indica Varma
• Acicularia intermedia Dragastan
• Acicularia jurassica J.H.Johnson
• Acicularia marginata L.Morellet & J.Morellet (uncertain)
• Acicularia mediopora Munier-Chalmas
• Acicularia michelini Munier-Chalmas ex L.Morellet & J.Morellet
• Acicularia micropora Munier-Chalmas ex L.Morellet & J.Morellet
• Acicularia miocaenica Reuss, 1861 (uncertain)
• Acicularia munieri L.Morellet & J.Morellet
• Acicularia parvula Munier-Chalmas ex L.Morellet & J.Morellet
• Acicularia pavantina d'Archiac, 1846 †
• Acicularia schenckii (K.Möbius) Solms-Laubach, 1895 accepted as Acetabularia schenckii K.Möbius, 1889 represented as Acetabularia subg. Acicularia schenckii K. Möbius, 1889
• Acicularia shenckii (Möbius) Solms-Laubach, 1895 (uncertain)
• Acicularia transylvana Bányai & Morellet
• Acroblaste reinschii Wille, 1890 accepted as Pilinia reinschii (Wille) Collins, 1908
• Acrochaete apiculata (Setchell & N.L.Gardner) O'Kelly, 2006
• Acrochaete cingens (Setchell & N.L.Gardner) C.J.O'Kelly, 2006 accepted as Ulvella cingens (Setchell & N.L.Gardner) R.Nielsen, C.J.O'Kelly & B.Wysor, 2013
• Acrochaete cladophorae (Hornby) R.Nielsen, 1995 accepted as Ulvella cladophorae (Hornby) A.C.Mathieson & Dawes, 2017
• Acrochaete codicola (Setchell & N.L.Gardner) O'Kelly, 2006 accepted as Ulvella codicola (Setchell & N.L.Gardner) R.Nielsen, C.J.O'Kelly & B Wysor, 2013
• Acrochaete endostraca R.Nielsen, 1988 accepted as Ulvella endostraca (R.Nielsen) R.Nielsen, C.J.O'Kelly & B. Wysor, 2013
• Acrochaete endozoica (W.M.Goldberg, J.C.Makemson & S.B.Colley) M.J.Wynne, 1986 accepted as Ulvella endozoica (Goldberg, Makemson & Colley) R.Nielsen, C.J.O'Kelly & B. Wysor, 2013
• Acrochaete flustrae (Reinke) O'Kelly, 2006 accepted as Epicladia flustrae Reinke, 1889
• Acrochaete geniculata (N.L.Gardner) O'Kelly, 1983
• Acrochaete heteroclada J.A.Correa & R.Nielsen, 1988 accepted as Ulvella heteroclada (Correa & R.Nielsen)R.Nielsen, C.J.O'Kelly & B.Wysor, 2013
• Acrochaete inflata (Ercegovic) Gallardo, Gómez Garreta, M.A.Ribera, Cormaci, G.Furnari, Giaccone & Boudouresque, 1993 accepted as Ulvella inflata (Ercegovic) R.Nielsen, C.J.O'Kelly & B. Wysor, 2013
• Acrochaete leptochaete (Huber) R.Nielsen, 1983 accepted as Ulvella leptochaete (Huber) R.Nielsen, C.J.O'Kelly & B.Wysor, 2013
• Acrochaete major (J.Feldmann) M.Perret-Boudouresque & H.Seridi, 1989 accepted as Entocladia major (Feldmann) R.Nielsen, 1972
• Acrochaete marchantiae (Setchell & N.L.Gardner) R.Nielsen & McLachlan, 1986 accepted as Ulvella marchantiae (Setchell & N.L.Gardner) R.Nielsen, C.J.O'Kelly & B Wysor, 2013
• Acrochaete operculata J.A.Correa & R.Nielsen, 1988 accepted as Ulvella operculata (Correa & R.Nielsen) R.Nielsen, C.J.O'Kelly & B.Wysor, 2013