Ultrastructure and small-subunit ribosomal DNA sequence of Henneguya lesteri n. sp (Myxosporea), a parasite of sand whiting Sillago analis (Sillaginidae) from the coast of Queensland, Australia

Henneguya lesteri n. sp, (Myxosporea) is described from sand whiting, Silla go analis, from the southern Queensland coast of Australia. H. lesteri disp lays a preference for the pseudobranchs and is typically positioned along t he afferent blood vessels, displacing the adjoining lamellae and disrupting their normal array, The plasmodia appeared as whitish-hyaline, elliptical cysts (mean dimensions 230 x 410 mum) attached to the oral mucosa lining of the hyoid arch on the inner surface of the operculum. Infections of the gi lls were also found, in which the plasmodia were spherical, averaged 240 x 240 mum in size and were located on the inner hemibranch margin. The parasi tes lodged in the gill filament crypts and generated a mild hyperplastic re sponse of the branchial epithelium, In histological sections, the plasmodiu m wall and adjoining ectoplasm appeared as a finely granulated, weakly eosi nophilic layer, Ultrastructurally, this section of the host-parasite interf ace contained an intricate complex of pinocytotic channels. H. lesteri is p olysporic, disporoblastic and pansporoblast forming. Sporogenesis is asynch ronous, with the earliest developmental stages aligned predominantly along the plasmodium periphery, and maturing sporoblasts and spores toward the ce nter. Ultrastructural details of sporoblast and spore development are in ag reement with previously described myxosporeans. The mature spore is drop-sh aped, length (mean) 9.1 mum, width 4.7 mum, thickness 2.5 mum, and comprise s 2 polar capsules positioned closely together, a binucleated sporoplasm an d a caudal process of 12.6 mum. The polar capsules are elongated, 3.2 x 1.6 mum, with 4 turns of the polar filament. Mean length of the everted filame nt is 23.2 mum, Few studies have analyzed the 18S gene-of marine Myxosporea . In fact, H. lesteri is the first marine species of Henneguya to be charac terized at the molecular level: we determined 1966 bp of the small-subunit (18S) rDNA, The results indicated that differences between this and the hit herto studied freshwater Henneguya species are greater than differences amo ng the freshwater Henneguya species.