Four new species of the genus Hatschekia Poche, 1902 (Copepoda: Siphonostomatoida: Hatschekiidae) are described based on female specimens collected from pufferfishes (Tetraodontiformes: Tetraodontidae) caught in coastal waters off the Ryukyu Islands, Japan: H. longiabdominalis sp. n. on Arothron hispidus (Linnaeus), H. geniculata sp. n. on A. hispidus (type host) and A. stellatus (Bloch et Schneider), H. ellipsocorpa sp. n. on A. mappa (Lesson), and H. boonah sp. n. on A. nigropunctatus (Bloch et Schneider) (type host) and A. meleagris (Schneider). Hatschekia longiabdominalis sp. n. and H. boonah sp. n. differ from all other congeners by sharing an unusual, projected abdomen and a fusiform trunk with posterior lobes; these two species are differentiated from each other by the shape of the dorsal chitinous frame on the cephalothorax. Hatschekia geniculata sp. n. can be distinguished by the combination of the following morphological characters: a rhomboidal cephalothorax with a pair of lateral conical protrusions, a cylindrical trunk with posterior lobes and a bent abdomen with a dorsal protrusion. Hatschekia ellipsocorpa sp. n. resembles H. pholas (Wilson, 1906) but can be distinguished from the latter by the possession of one distal and one inner setae on the terminal endopodal segment of legs 1 and 2. Hatschekia pholas is also redescribed based on female specimens from the tetraodontid A. stellatus. At present, 44 nominal species of the genus have been reported from Japan, including four new species described in this paper; 38 of them have been described originally from Japan.
During surveys of parasites of the whitemouth croaker Micropogonias furnieri (Desmarest) and the mullet Mugil platanus Günther from Samborombón Bay, Argentina, Trichodina puytoraci, T. lepsii, T. jadranica, T. murmanica, Diparitella simplex and Trichodina scalensis sp. n. were morphologically studied. Taxonomic and morphometric data for these trichodinids based on dry silver nitrate-impregnated specimens are presented. This study is the first formal report of these trichodinids from the southwest Atlantic Ocean, and the description of a new species from M. platanus.