Isymenia flabellata J. Agardh, 1899: 66 (type locality: Guadeloupe, West Indies).
Sebdenia flabellata (J. Agardh) Parkinson, 1980: 12.—Millar, 1990: 328.— Huisman, 1993: 16.
Halymenia agardhii De Toni, 1905: 1542.—Barratt et al., 1984: species list.
Taxonomic synonym:
* Halymenia polydactyla Børgesen, 1932b: 122–124, fig. 10, pl. IV (type locality: Port Okha, Gujarat, India).—Børgesen, 1934b: 35.— P. Anand, 1943b: 17.— Lind, 1956: 26.— Durairatnam, 1961a: 54, pl. XI: fig. 7; pl. XII: fig. 3.— Salim, 1965: 193.— S. Dixit, 1966: 14.— Lawson, 1980: 49.— Ohno & Mairh, 1982: table 1.— Untawale, Dhargalkar, & Agadi, 1983: [39].— R. Qasim & Barkati, 1985: table 2.— Shameel & J. Tanaka, 1992: 47.
Sebdenia polydactyla (Børgesen) M. Balakrishnan, 1961a: 89–90.—M. Balakrishnan, 1961c: 202–212, figs. 28–41, pl. VI: figs. 1, 2.— K. Srinivasan, 1965: 246.— K. Srinivasan, 1969: 14, figs. 1–3, pl. XIV.— Gopalakrishnan, 1970: 64.— V. Krishnamurthy & H. Joshi, 1970: 20.— Gopalakrishnan, 1971: tables II, IV.— Chauhan & Mairh, 1978: 35.— Murthy, Bhattacharya, & Radia, 1978: 382.— Lawson, 1980: 60.— R. Qasim, 1980: table 1.— R. Qasim, 1981: tables 1, 2.— Untawale, Dhargalkar, & Agadi, 1983: [31].— R. Norris & Aken, 1985: 56, fig. 4.— R. Qasim, 1986: tables 1, 4.— M. Dave et al., 1987: table 1.— Shameel, 1987a: 514.— Shameel & Afaq Hussain, 1987: 297.— Pandya, Bapodra, & Parekh, 1990: 557.— R. Parekh & Chauhan, 1990: table 1.
INDIAN OCEAN DISTRIBUTION: Australia, India, Kenya, Oman, Pakistan, South Africa, Sri Lanka.
Note: When transferring Isymenia flabellata to Halymenia, De Toni (l.c.) changed the epithet to agardhii because of the prior existence of H. flabellata Schmitz (1895a: 140, 162–163). Although various authors, beginning with Børgesen (1932b: 123), have noted the similarity of Sebdenia polydactyla to S. flabellata, the conspecificity of the taxa remains to be demonstrated by a comparison of type specimens. Millar (1990: 328, 329) has placed in the synonymy of S. flabellata two species originally described from Borneo Bank and not recorded from the Indian Ocean: Halymenia arachnophylloidea Weber-van Bosse (1921: 239, fig. 74) and H. tubulosa Weber-van Bosse (1921: 238, fig. 73).