Ceratothoa retusa (Schiœdte & Meinert, 1883) (Isopoda, Cymothoidae), a variable species of fish parasitic marine isopod from the Indian Ocean

Ceratothoa retusa (Schiœdte & Meinert, 1883) is redescribed from the lectotype (here designated) collected from Mozambique, and the range is extended to include the Gulf of Suez in the Red Sea. Ceratothoa retusa is distinctive within the genus with a manifestly small head deeply immersed into pereonite 1, which has prominent, but variable, projecting anterolateral margins. Ceratothoa retusa has a tropical and subtropical Indian Ocean distribution, extending from eastern Africa (and now the Red Sea) eastwards to northern Australia and Indonesia. The only known hosts are the halfbeaks, Hemiramphus far (Forsskål, 1775) and H. robustus Günther, 1866 (Hemiraphidae)