An attempt was made to infer the phylogeny of Pseudo-nitzschia species by using the mitochondrial-encoded gene, cytochrome c oxidase subunit I (cox1), and comparing it with the nuclear-encoded large subunit ribosomal DNA (LSU rDNA). A pair of primers targeting Pseudo-nitzschia cox1 was designed in silico and used to infer the molecular phylogeny of Pseudo-nitzschia. The primer pair was tested using genomic DNAs isolated from six species of Pseudo-nitzschia from Malaysia. The phylogenetic inference of cox1 was then compared to the LSU rDNA phylogeny. Phylogenetic reconstructions of both data sets revealed monophyly of Pseudo-nitzschia species complexes. The range of genetic divergences among Pseudo-nitzschia species were higher in the cox1 data set (3.5–20.4 %) compared to the LSU rDNA data set (0.1–8.8 %). The present study suggests that high genetic divergence in cox1 of Pseudo-nitzschia species could be a useful genetic marker for DNA bar coding.

Paradilepis scolecina (Rudolphi, 1819) Hsü, 1935 is a tapeworm widely distributed across the globe that uses piscivorous birds as definitive hosts. Although various piscivorous birds inhabit the Republic of Korea (Korea), this species has not previously been documented in the country. In this study, we report its occurrence in resident great cormorants, Phalacrocorax carbo sinensis (Staunton, 1796), based on integrated morphological, molecular, and ultrastructural analyses. The recovered specimens exhibited 20 rostellar hooks of parvoid type arranged in a double row consistent with the scolecina pattern, allowing distinction from other congeners. Partial LSU sequences of the specimens in this study showed the highest identity to P. scolecina isolates from South Africa and Lithuania (GenBank accession no. MH062156 & PQ570010, 100% identity), while SSU sequences were closest to Paradilepis sp. references (MH699816, 98.1%). Combined BLAST and phylogenetic analyses supported their identification as P. scolecina. Notably, scanning electron microscopy revealed a previously undescribed cirrus surface featuring rose-thorn–shaped spines interspersed with capilliform filitriches—representing the first such ultrastructural description within the family Gryporhynchidae. The shift of Ph. c. sinensis increasing tendency toward year-round residency in Korea may enhance parasite transmission by increasing contact with local freshwater hosts, a hypothesis that warrants further ecological investigation. Additionally, the presence of P. scolecina may have implications for wild fish populations and nearby aquaculture facilities, particularly if intermediate or paratenic hosts include economically important species. These findings contribute to the growing knowledge of the parasite fauna of cormorants in Korea and underscore the need for further research into the transmission dynamics and host range of trophically transmitted cestodes in East Asian freshwater ecosystems.

Highlights •First study investigating ciguatera-causing organisms in Seychelles, southwestern Indian Ocean.•Gambierdiscus belizeanus identified using combined morphological and molecular approaches.•Isolation of a G. belizeanus strain exhibiting low ciguatoxin-like activity.•Evidence of intraspecific variability in toxin production among G. belizeanus strains from the same locality.

Although the taxonomy of oligotrich ciliates has been widely investigated, yet the species diversity remains poorly known. We newly designed a pair of oligotrich-specific LSU rDNA primers covering the 600-bp D1/D2 region, and it was effective for detecting oligotrich species. Using the primers, we constructed the cloning libraries to investigate the species diversity of oligotrichs in the northern coastal waters of the South China Sea. In total, 165 oligotrich sequences were obtained from five widely separated sampling sites. Sixty operational taxonomic units (OTUs) were obtained at 99% similarity threshold, and low-abundance OTUs with no more than two sequences contributed most of these (about 78%). Our findings are consistent with previous morphological studies, Strombidium was found the most abundant and widely distributed genus in this area. In addition, the BLAST search in the NCBI database resulted in 95% OTUs matching with named oligotrich species in similarity below 99%. Therefore, oligotrich morphospecies diversity has been underestimated as low-abundance species, and the LSU rDNA oligotrich sequence database needs to be better promoted.

The marine dinoflagellate Amphisolenia bidentata possesses complete intracellular symbionts of prokaryotic and eukaryotic origin. This was confirmed ultrastructurally little over 20 years ago when it was showed that the eukaryotic endosymbiont had a nucleus, a chloroplast and mitochondria. We collected Amphisolenia bidentata cells in the Indian Ocean and the identity of the eukaryotic endosymbionts was investigated using both microscopical and molecular methods. Individual specimens of Amphisolenia bidentata were identified by light microscopy and selected for single-cell PCR. Host and endosymbiont nuclear-encoded LSU and SSU rDNA sequences were determined by PCR cloning. Blast searches showed the endosymbiont LSU sequence to have affinity to Pelagophyceae, an algal class within Chromalveolata that also includes dinoflagellates. Since more SSU rDNA sequences from pelagophytes are available we performed a SSU based phylogeny of chromalveolates. The eukaryotic endosymbiont clustered within a clade comprising flagellated and coccoid pelagophytes whereas Amphisolenia bidentata formed a sister taxon to other dinophysioids. Molecular data therefore resolved the endosymbiont in A. bidentata being a pelagophyte and thus identified the ninth novel chloroplast type in dinoflagellates and a new species association. Based on sequence divergence estimates and phylogenetic inference the endosymbiont in A. bidentata likely represents an undescribed genus of pelagophytes.

Food poisoning caused by consuming raw horsemeat contaminated with Sarcocystis is a significant public health concern. Two morphotypes of sarcocysts in horsemeat, characterized by upright and folded villar protrusions, are typically identified as Sarcocystis fayeri and S. bertrami , respectively. However, recent molecular studies focusing on the ribosomal RNA gene (rDNA) and mitochondrial cytochrome c oxidase subunit I gene (cox1) have indicated a conspecific relationship between these two morphotypes using a limited number of specimens. To explore further genetic diversity in equid sarcocysts, cox1 and large-subunit (LSU) rDNA sequences were analyzed in sarcocysts extracted from horsemeat inspected from 150 horses (76 and 41 horses imported from Canada and France, respectively, and 33 horses reared in Japan). Sarcocysts were detected in the muscles of 71, 2, and 3 horses from Canada, France, and Japan, respectively. Fifty-eight sarcocysts underwent cox1 and the LSU rDNA sequencing. Newly obtained cox1 sequences (n = 53) and sequences labeled as equid S. bertrami , S. fayeri and S. asinus retrieved from GenBank (n = 53) exhibited conspecific relationships. Inter-individual variation in cox1 sequences was observed among various sarcocysts, even within a single host animal, although no intra-individual variation was observed. However, nuclear-embedded mitochondrial DNA (NUMT: cox1 pseudogene) sequences were obtained using inappropriate techniques using certain primers. The LSU rDNA of sarcocysts (211 cloned sequences from 54 sarcocysts) exhibited inter-individual and robust intra-individual variations, indicating significant intragenomic rRNA array mosaicism in S. bertrami. These findings confirmed the conspecificity of classically defined species without geographical subpopulations. [Display omitted] • Notably divergent cox1 and LSU rDNA sequences of Sarcocystis bertrami in horses. • Mitochondrial cox1 is a reliable molecular marker for specific identification. • PCR amplification of cox1 pseudogene segments misleads specific identification. • Nuclear rRNA array mosaicism causes divergent rDNA sequences in Sarcocystis spp. [ABSTRACT FROM AUTHOR]