Four species of monocotylid monogeneans were found on a spotted eagle ray Aetobatus cf. narinari caught off Noumea, New Caledonia, South Pacific. The host is illustrated for future possible identification, because it belongs to a currently unresolved species complex. Decacotyle octona (Young, 1967) Chisholm & Whittington, 1998, from the secondary gill lamellae, is figured and previously unreported details of the reproductive system are described. D. elpora n. sp. is described from numerous specimens found between the secondary gill lamellae. The new species, 780-1650 microm in body length, is smaller than D. octona, but has a longer sclerotised male copulatory organ. It is characterised by two dorsal haptoral accessory structures, each with three bumps, and a 9-shaped sclerotised male copulatory organ 240-290 microm in length. D. octona and Clemacotyle australis Young, 1967, both from the branchial cavity, and Thaumatocotyle pseudodasybatis Hargis, 1955, from the nasal tissue, are new geographical records for New Caledonia. It is suggested that differences in the monocotylid fauna between the Atlantic and Indo-Pacific forms of Aetobatus cf. narinari could be of interest for the systematic status of the ray, but the sporadic nature of the sampling probably casts doubt on the usefulness of the currently available data.