Several small-sized and discoid naviculoid diatoms, close to Cocconeiopsis (Bacillariophyta, Biraphidineae), were found on the teguments of Holothuria atra (Juan de Nova lagoon, 17° 02.797'S; 42° 43.811' E, Scattered Islands, Mozambique Channel). These taxa were apparently absent from the macroalgae and sediments of the same site. The taxa are illustrated in LM (light microscopy) when possible and SEM (scanning electron microscopy), and compared to species of Cocconeiopsis and similar genera. The new taxa are temporarily classified under the genus Cocconeiopsis, but their membership in another genus or to a new genus is discussed. Cocconeiopsis juandenovensis sp. nov. was rather rare on the sea-cucumber teguments, two other taxa were very rare. All have relatively similar features (length, striation), but their SEM characteristics are distinct enough to separate them as different taxonomic entities. The epizoic diatom sample was composed of more than 12 genera. The new taxa were not observed in previous marine surveys in Mascarenes. An epizoic affinity of these taxa with the holothurian host is conceivable.