Highlights •LSU ribosomal RNA is the ribozyme that catalyzes translation.•Variation in its GC content was measured across regions of the ribosome, in many Bacteria, Eukaryota, Archaea.•GC variation across taxa increases, smoothly, from the deep to the superficial regions.•This reflects the in-out pattern of increasing variation of all the nucleotides (A, C, G, T).•This GC mapping will help to improve models used for phylogenetic-tree reconstruction.

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Calcareous sponges are taxonomically difficult, and their morpho-systematic classification often conflicts with molecular phylogenies. Consequently, species descriptions that rely solely on morphological characters,and taxonomic revisions appear to provide little to no information about phylogenetic affiliations and integrative approaches, combining DNA and morphological data, are applied more frequently. However, a standardized database that combines DNA sequence and morphological specimen information is still missing for calcareous sponges. The mitochondrial cytochrome oxidase subunit 1 gene (COI) is the marker of choice for rapid species identification in many other animal taxa, including demosponges, for which COI sequences and morphological information have been compiled in the sponge barcoding database (). But due to the peculiarities of calcarean mitochondrial genomes, sequencing COI in Calcarea is methodologically challenging. We here propose the use of one more commonly used DNA marker, the C-region of the 28S gene (LSU), as standard barcoding marker for Calcarea, after also considering the internal transcribed spacer (ITS) region for such proposes. Especially in the subclass Calcaronea, we observed severe problems of high intra- and intergenomic variation that impedes pan-calcarean ITS alignments. In contrast, the C-region of LSU provides a short but phylogenetically informative DNA sequence, alignable across both subclasses with the help of a newly developed secondary structure and which also can be used to address exemplary taxonomic questions. With our work, we start to close the gap of Calcarea in the sponge barcoding project () and provide a resource for biodiversity studies and potentially for DNA-guided species identification.

No summary available.

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.