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A new species of the cyclopoid copepod genus Ergasilus von Nordmann, 1832 is described based on material collected from the gills of an elasmobranch, Himantura oxyrhyncha (Sauvage, 1878), collected in the Java Sea off the coast of West Kalimantan, Indonesia. To justify the establishment of the new species, Ergasilus kimi sp. nov., detailed comparisons are made with the 28 congeneric species that share the combination of a 3-segmented leg 1 endopod and the presence of 2 setae on the free exopodal segment of leg 5. This is the fourth report of an Ergasilus species infecting an elasmobranch and it is concluded that each represents an independent colonization event of elasmobranchs as hosts.

The olfactory sacs of 488 specimens belonging to 18 species of rajid and arhynchobatid skates from the Argentine Sea were sampled for parasites. No parasitic copepods were found in 11 host species, but siphonostomatoid specimens referable to Kroeyerina Wilson, 1932 (Kroyeriidae) and Brianella corniger Wilson, 1915 (Lernaeopodidae) were found on the spotback skate Atlantoraja castelnaui (Miranda Ribeiro, 1907), the smallnose fanskate Sympterygia bonapartii Müller & Henle, 1841, the bignose fanskate Sympterygia acuta Garman, 1877 and the zipper sand skate Psammobatis extenta (Garman, 1913) (Rajiformes: Arhynchobatidae). Additionally, specimens of B. corniger were found in the olfactory sacs of the Rio skate Rioraja agassizii (Müller & Henle, 1841) and attached to the pectoral fins of the Magellan skate Bathyraja magellanica (Philippi, 1902) and the smallthorn sand skate Psammobatis rudis Günther, 1870. A new species, Kroeyerina sudamericana sp. nov., is described and illustrated. The new species most closely resembles Kroeyerina nasuta Wilson, 1932, but can be distinguished from it by the different armature of the antennule, a proportionally shorter genital complex and the chela of the antenna which, when closed, leaves a gap between the corpus and claw, the latter having no spines. The new species represents the first record of Kroeyerina in South American marine waters. The present study also extends the distribution range of B. corniger, previously known only from the Pacific, to include Atlantic waters, and records seven new host species, all of which are members of the Arhynchobatidae.

The genus Schistobrachia Kabata, 1964 (Lernaeopodidae: Siphonostomatoida) currently accommodates five species of which two infect holocephalans and three utilize elasmobranchs. Kensley & Grindley (1973) reported three females from "Dipturus batis" (Linnaeus, 1758) collected in Table Bay, South Africa, which they assigned to S. ramosa (Krøyer, 1863), a species previously known only from the North Atlantic. Re-examination of these specimens (labelled Charopinus ramosus Krøyer, 1863 and deposited in the Iziko South African Museum) and additional Schistobrachia material newly collected from the gills of various Rajiformes off the South African west and south coasts, showed that Kensley & Grindley's (1973) earlier record of S. ramosa was misidentified and in reality represents a distinct species, S. kabata sp. nov. Both sexes of the new species are described using light and/or scanning electron microscopy.

Acanthobothrium ningdense n. sp. and Acanthobothrium guanghaiense n. sp. are described from the spiral intestine of the whip stingray, Dasyatis akajei (Müller & Henle). Acanthobothrium ningdense n. sp. is reported based on 38 cestode specimens collected at five locations along the Chinese coast, i.e. Taizhou, Zhejiang Province, Ningde and Xiamen, Fujian Province, Taishan, Guangdong Province and Sanya, Hainan Province between 2012 and 2015. Acanthobothrium ningdense n. sp. belongs to the "species category 4" characterised by Ghoshroy & Caira. Among category 4 Acanthobothrium species, A. ningdense n. sp. most closely resembles A. micracantha Yamaguti, 1952 and A. latum Yamaguti, 1952, both from the same host species. Acanthobothrium ningdense n. sp. differs from A. micracantha by lacking a long robust hook handle that connects the bases of medial and lateral hooks, and from A. latum by having much longer axial prongs than abaxial prongs. Acanthobothrium guanghaiense n. sp., only found in Taishan, Guangdong Province in 2014, is a category 2 Acanthobothrium species. Among category 2, A. guanghaiense n. sp. most closely resembles A. semnovesiculum Verma, 1928, but can be differentiated from it by the arrangement of testes (in two staggered columns rather than in two tandem columns), and the shape of abaxial prong (nearly straight instead of with a conspicuous curve in the proximal portion). Acanthobothrium macrocephalum Wang & Yang, 2001 is redescribed based on new specimens collected from D. akajei in Guanghai and Sanya. With this study, the total number of Acanthobothrium species reported from D. akajei is brought to nine. It is possible that some of the species of Acanthobothrium previously reported from D. akajei not encountered in this study may have geographically restricted distributions, as was observed here for A. guanghaiense n. sp..