Experimental infection of rainbow trout Oncorhynchus mykiss (Walbaum) with the monogenean Discocotyle sagittata (Leuckart, 1842) allowed comparison between trickle and single exposure, two infection modes demonstrated to occur in the wild. Both types of infection resulted in mean larval attachment success around 50%, which was significantly dependent on dose of infective larvae used (P < 0.0001), but was not affected by mode of infection (P = 0.244). Worms recovered from fish exposed to the same number of oncomiracidia but different mode of infection differed in their rate of development. The developmental stage attained by parasites was significantly affected by number of infective larvae used (P = 0.005), and by the interaction between dose and mode of infection (P = 0.026), suggesting competition among attached larvae. Statistical analysis demonstrated that in the early stages of infestation, worm distribution over the gill arches can be explained by the relative amount of water flowing over them. One, two and three months post-infection parasite numbers were comparable (P = 0.805), but their observed distribution gradually decreased in gill arches III and IV and increased in gill arch I, suggesting that parasites migrate after initial attachment. These results reproduce phenomena observed in the field, indicating that the experimental infection system could be employed to study infection dynamics and host-parasite interactions under controlled conditions.
Myliocotyle borneoensis sp. n. and M. multicrista sp. n. (Monocotylidae: Heterocotylinae) are described from the gills of the mottled eagle ray, Aetomylaeus maculatus (Gray), and the banded eagle ray A. nichofii (Bloch et Schneider) (Myliobatidae), respectively, collected from the northern coast of Malaysian Borneo. These are the first monogeneans to be described on elasmobranchs from Borneo. The formerly monotypic Myliocotyle (for M. pteromylaei) was distinguished from other monocotylids by the distribution and morphology of the eight sclerotised dorsal haptoral accessory structures and the morphology of the male copulatory organ. However, we have determined that M. pteromylaei has ten structures on the dorsal surface of the haptor. Myliocotyle borneoensis is distinguished from M. pteromylaei by the morphology of the male copulatory organ and its accessory piece. Myliocotyle multicrista has 12 sclerotised dorsal haptoral accessory structures and a male copulatory organ with two accessory pieces. Additional sclerotised ridges across the ventral surfaces of each loculus (except the posterior-most pair) are also present in M. multicrista. The diagnosis for Myliocotyle is revised given our discovery of additional dorsal haptoral accessory structures in the type species and to accommodate other new characters of the two new species. Anterior secretions of Myliocotyle are discussed.
Two new species of entobdelline (capsalid) monogeneans are described from the skin of Australian dasyatid stingrays, namely Neoentobdella cribbi sp. n., a small parasite from the estuarine stingray, Dasyatis fluviorum Ogilby (Elasmobranchii: Dasyatidae) and Neoentobdella baggioi sp. n., a relatively large parasite from the porcupine ray, Urogymnus asperrimus (Bloch et Schneider) (Elasmobranchii: Dasyatidae). A striking feature of both of these new parasite species is a pad, possibly located within the genital atrium, armed with rows of closely spaced, rod-shaped microsclerites. Both species also possess a muscular papilla in the genital tract and a club-shaped structure near the common genital opening on the left lateral margin of the body. In N. cribbi, the latter feature is large and located anterior to the genital pad and in N. baggioi, it is small and located in a more posterior position. Similar embellishments in the genital area occur in N. natans Kearn et Whittington, 2005 and in N. parvitesticulata Kearn et Whittington, 2005, while other species (e.g. N. garneri Whittington et Kearn, 2009 and N. taiwanensis Whittington et Kearn, 2009) lack these features and differ also in functional aspects of the male copulatory apparatus and the haptor. Separate generic status for these two groupings is indicated, but must await a comparative and comprehensive review of all Neoentobdella spp.
The ‘buccal complex’ of Pricea multae Chauhan, 1945 consists of two buccal suckers, the pharynx, a putative taste organ and the mouth cavity. The two suckers are dorsal to the mouth cavity, and the pharynx posterior to them. The septum in each sucker consists of connective tissue containing muscle filaments, lined by tegument with short irregular microvilli. The mouth cavity and the lumen of the suckers are lined by tegument with short irregular lamellae and by tegument with long bulbous, interconnected lamellae, separated from each other and from the body surface tegument by septate junctions. A ventral extension of the mouth cavity is also lined by tegument with short irregular lamellae. An anterior ‘taste organ’ is lined by ‘normal’ (body) tegument and tegument with short irregular lamellae. Glandular ducts open into it, and it contains many small uni-ciliate and multiciliate receptors, as well as two receptor complexes each consisting of a large non-ciliate receptor surrounded by small and large uniciliate receptors, with multiciliate receptors closeby. The four types of receptors are described in detail. The anterior part of the pharyngeal lumen is lined by an epithelium with dense surface lamellae and is penetrated by non-ciliate receptors. Attention is drawn to significant differences between the buccal complexes of the polyopisthocotylean monogeneans Pricea multae (Gastrocotylidae), Gotocotyla secunda (Tripartii, 1956) (Gastrocotylidae), Pulylabroides australis (Murray, 1931) (Microcotylidae), Zeuxapia serialae (Meserve, 1938) (Axinidae) and Diclidophora merlangi (Kuhn, 1832) (Diclidophoridae).