Note: The taxonomic and nomenclatural history of the Spongomorpha-Acrosiphonia complex is discussed in the appended Taxonomic and Nomenclatural Notes. We distinguish the two genera on the basis of nuclear number, assigning species with uninucleate cells to Spongomorpha (none reported from the Indian Ocean) and those with multinucleate cells to Acrosiphonia.
Conferva arcta Dillwyn, 1809 [1802–1809]: 67, suppl. pl. E (type locality: Bantry Bay, Ireland).
Spongomorpha arcta (Dillwyn) Kützing, 1854: 16.—Nizamuddin & Begum, 1973: 12–13, figs. 73, 74.— Shameel & J. Tanaka, 1992: 24.
Acrosiphonia arcta (Dillwyn) Gain, 1912: 31.
INDIAN OCEAN DISTRIBUTION: Pakistan.