The following two taxa apparently lie within the circumscription of Hydrolithon onkodes but have not yet been transferred or reduced to synonymy:
Lithophyllum funduense Pilger, 1908b: 42, pl. 5: figs. 4–7 (type locality: Fundo Island, Pemba, Tanzania).—De Toni, 1924: 674.— Adey & Lebednik, 1967: 47.
Lithophyllum onkodes (Heydrich) Heydrich forma funduense (Pilger) Foslie, 1909: 38, 40 (`oncodes forma funduensis').—Foslie, 1929: 36, pl. LXVII: figs. 1, 2.
INDIAN OCEAN DISTRIBUTION: Tanzania.