Short communication: New data support phylogeographic patterns in a marine parasite Tristriata anatis (Digenea: Notocotylidae)

Elucidation of Himasthla leptosoma (Creplin, 1829) Dietz, 1909 (Digenea, Himasthlidae) life cycle with insights into species composition of the north Atlantic Himasthla associated with periwinkles Littorina spp

Trematodes of the genus Himasthla are usual parasites of coastal birds in nearshore ecosystems of northern European seas and the Atlantic coast of North America. Their first intermediate hosts are marine and brackish-water gastropods, while second intermediate hosts are various invertebrates. We analysed sequences of partial 28S rRNA and nad1 genes and the morphology of intramolluscan stages, particularly cercariae of Himasthla spp. parasitizing intertidal molluscs Littorina spp. in the White Sea, the Barents Sea and coasts of North Norway and Iceland. We showed that only three Himasthla spp. are associated with periwinkles in these regions. Intramolluscan stages of H. elongata were found in Littorina littorea, of H. littorinae, in both L. saxatilis and L. obtusata, and of Cercaria littorinae obtusatae, predominantly, in L. obtusata. Other Himasthla spp. previously reported from Littorina spp. in North Atlantic are either synonymous with one of these species or described erroneously. Based on a comparison of newly generated 28S rDNA sequences with GenBank data, rediae and cercariae of C. littorinae obtusatae were identified as belonging to H. leptosoma. Some previously unknown morphological features of young and mature rediae and cercariae of the three Himasthla spp. are described. We provide a key to the rediae and highlight characters important for identification of cercariae. Genetic diversity within the studied species was only partially determined by their specificity to the molluscan host. The nad1 network constructed for H. leptosoma lacked geographical structure, which is explained by a high gene flow owing to highly vagile definitive hosts, shorebirds.

Characterization of the complete mitochondrial genome of Notocotylus sp. (Trematoda, Notocotylidae) and its phylogenetic implications

The parasite genus Notocotylus comprises at least 50 species colonizing mainly aquatic birds and to a lesser extent some mammals, particularly rodents. Here trematode specimens isolated from a wild black swan were characterized and identified to belong to the genus Notocotylus via morphological and molecular analyses. Phylogenetic position of the isolate among other trematodes was determined based on the ribosomal internal transcribed spacer (ITS) 1 and 2. The complete mitochondrial (mt) genome of the isolate was amplified, sequenced, assembled, analyzed, and annotated. The isolate has an AT-rich mt genome (14,317 bp in length) that comprises 12 protein-coding genes (PCGs), 22 transfer RNA genes, and two ribosomal RNA genes. The Notocotylus isolate identified in this study has relatively high mt genome sequence identity and identical gene content and arrangement to a known Notocotylidae species, Ogmocotyle sikae. The isolate formed a genetic clade with O. sikae in phylogenetic analysis of the concatenated PCG amino acid sequences. Compared to the ITS, the trematode mt genome appears more informative for resolving high-level phylogenies. To the best of our knowledge, this is the first study exploring the complete mt genome for the genus Notocotylus, and it offers a novel genomic resource that has important implications for trematode phylogenetics.

It is marine: distinguishing a new species of Catatropis (Digenea: Notocotylidae) from its freshwater twin

The morphology of sexual adults is the cornerstone of digenean systematics. In addition, life cycle data have always been significant. The integration of these approaches, supplemented with molecular data, has allowed us to detect a new species that many researchers may have previously seen, but not recognized. Sexual adults from common eiders that we found in northern European seas were extremely similar to other notocotylids, but the discovery of their intermediate host, a marine snail, revealed the true nature of this material. Here we describe sexual adults, rediae and cercariae of Catatropis onobae sp. nov. We discuss how 'Catatropis verrucosa' should be regarded, justify designation of the new species C. onobae for our material and explain why it can be considered a cryptic species. The phylogenetic position of C. onobae within Notocotylidae, along with other evidence, highlights the challenges for the taxonomy of the family, for which two major genera appear to be polyphyletic and life cycle data likely undervalued.