A new species and emendation of the seldom reported Enterohaematotrema Mehra, 1940 (Digenea: Schistosomatoidea), including a revised phylogenetic hypothesis for turtle blood flukes

FOREGUT ULTRASTRUCTURE OF ADULT SANGUINICOLA VOLGENSIS (RAŠÍN, 1929) MCINTOSH, 1934 (DIGENEA: APOROCOTYLIDAE)

Herein, we use scanning and transmission electron microscopy to describe the foregut (mouth, pharyngeal canal, and associated epithelia and musculature) of an adult freshwater fish blood fluke, Sanguinicola volgensis (Rašín, 1929) McIntosh, 1934, infecting the blood of sabre, Pelecus cultratus Linnaeus, 1758 (Cypriniformes: Leuciscidae) from the Volga River, Russia. Our results indicate that S. volgensis has a pharynx and lacks an oral sucker and that its pharyngeal canal acts as a peristaltic pump that sucks blood into the esophagus, whereupon digestion commences with granules secreted from the esophageal epithelium. We saw no evidence of longitudinal muscle fibers beneath the pharyngeal canal epithelium, pharyngeal glands, or pharyngeal epithelial cells or muscle cells within the pharyngeal muscular complex; collectively indicating the presence of a pharynx rather than an oral sucker. The specialized epithelial lining associated with the mouth and pharyngeal canal evidently is unique among neodermatans; it is smooth, ∼40 nm thick anteriorly, and thickens (∼250-700 nm) posteriorly as the mouth cavity transitions into the pharyngeal canal. The pharyngeal canal epithelium has lumps of dense material resembling those of the basal lamina and fibrous coat of the tegument. The actin-like material within the pharyngeal cavity epithelium could provide structural support to the pharynx.

Morphological features of the testis of freshwater blood flukes of the genus Sanguinicola Plehn, 1905, with consideration of the testicular patterns in the Aporocotylidae

This is the first detailed study assessing the morphological features of the testis and testicular sperm of members of the freshwater blood flukes Sanguinicola sp. from Leuciscus idus (Cyprinidae) and for S. volgensis from Pelecus cultratus (Cyprinidae), and the marine blood fluke Aporocotyle simplex from Hippoglossoides platessoides (Pleuronectidae). The present study reports a unique feature in the distribution of germinal cellular components in freshwater Sanguinicola sp., showing the presence of the individual spermatocytes or their clusters in the testicular lobes, and the gathering of spermatid rosettes and spermatozoa within middle testicular lumen, which extends along the entire length of the testis. In contrast, each testis of marine A. simplex contains the usual mixed distribution of germ cells at various stages of development. The first TEM data on spermatozoon character of studied species has shown, unusual for digenean sperm structure, the absence of cortical microtubules in sperm principal region. Moreover, a variation in axoneme patterns is revealed in the studied aporocotylids, belonging to the different aporocotylid lineages a 9 + 0 axonemal type observed for freshwater teleost-infective species, Sanguinicola sp. and S. volgensis, and a 9 + '1' axonemal type revealed in spermatozoa of marine teleost-infective species A. simplex. The results discussed with the published data on the digenean sperm structure and the testicular patterns in the Aporocotylidae likely represent additional characteristics supporting the divergent evolutionary lineages of freshwater and marine aporocotylids. We anticipate future morphological studies of the sperm structure in aporocotylids of three lineages for an understanding of their phylogenetic relationships.