Research on complete mitochondrial genomes can help in understanding the molecular evolution and phylogenetic relationships of various species. In this study, the complete mitogenome of Hua aristarchorum was characterized to supplement the limited mitogenomic information on the genus Hua. Three distinct assembly methods, GetOrganelle, NovoPlasty and SPAdes, were used to ensure reliable assembly. The 15,691 bp mitogenome contains 37 genes and an AT-rich region. Notably, the cytochrome c oxidase subunit I (COX1) gene, commonly used for species identification, appears to be slow-evolving and less variable, which may suggest the inclusion of rapidly evolving genes (NADH dehydrogenase subunit 6 [ND6] or NADH dehydrogenase subunit 2 [ND2]) as markers in diagnostic, detection, and population genetic studies of Cerithioidea. Moreover, we identified the unreliability of annotations (e.g., the absence of annotations for NADH dehydrogenase subunit 4L [ND4L] in NC_037771) and potential misidentifications (NC_023364) in public databases, which indicate that data from public databases should be manually curated in future research. Phylogenetic analyses of Cerithioidea based on different datasets generated identical trees using maximum likelihood and Bayesian inference methods. The results confirm that Semisulcospiridae is closely related to Pleuroceridae. The sequences of Semisulcospiridae clustered into three clades, of which H. aristarchorum is one; H. aristarchorum is sister to the other two clades. The findings of this study will contribute to a better understanding of the characteristics of the H. aristarchorum mitogenome and the phylogenetic relationships of Semisulcospiridae. The inclusion of further mitochondrial genome sequences will improve knowledge of the phylogeny and origin of Cerithioidea.

In this study, we conducted morphological and molecular analyses of Perinereis wilsoni, a species being considered for aquaculture in China. We found this species difficult to identify because of its close morphological similarity to the sympatric P. mictodonta and thus sought genetic markers to more easily distinguish it and to investigate its phylogenetic relationship to P. mictodonta and other nereidids. For the first time, we sequenced, assembled, and annotated the complete mitochondrial genome, nuclear ribosomal sequences (18S-ITS1-5.8S-ITS2-28S), and four nuclear histone genes (H3-H2A-H2B-H4) of P. wilsoni. Comprehensive bioinformatics methods were employed to assemble the genome-skimming data of P. wilsoni to ensure assembly quality. Phylogenetic analyses based on five datasets of the available mitochondrial genomes (32 taxa in Nereididae, including 8 taxa in Perinereis), using maximum likelihood and Bayesian analyses, provide support for the monophyly of the genus Perinereis. In contrast, the P. nuntia species group, a subgroup within Perinereis, is nonmonophyletic. Perinereis wilsoni has a closer phylogenetic relationship with P. vancaurica and P. nuntia. Our study serves as a baseline for future work on the cultivation, reproductive biology, and phylogeny of P. wilsoni.

The complete mitochondrial genome and phylogenetic analysis for Leiognathus equula from the South China Sea was performed using shallow genome skimming. For accurate species identification and redescription, morphometric and meristic characters were examined and compared with previous descriptions. To facilitate the identification of species and to enable comparison with the mitochondrial genome phylogeny, molecular comparisons were conducted using three mitochondrial genes: large ribosomal RNA (16S rRNA), cytochrome c oxidase subunit 1 (COX1), and NADH dehydrogenase (ND5). The mitogenome (16 398 bp) comprised 38 mitochondrial genes, similar to most bony fishes: 13 protein-coding genes (PCGs), 2 rRNA and 22 transfer RNA genes, and 1 non-coding region. The complete mitogenome comprised 30.7% A, 24.2% T, 15.0% G, and 30.1% C. The A+T content (54.9%) was higher than the G+C content (45.1%). All PCGs started with the typical ATG codon, except COX1, which started with GTG. Seven PCGs ended with incomplete stop codons (TA or T). The Ka/Ks ratios of all PCGs were < 1, indicating purifying selection. The phylogenies of Leiognathidae, both based on the amino acid sequences of the 13 PCGs and the single genes 16S RNA and COX1, were monophyletic with high nodal support (> 75%). L. brevirostris (NC 026232) is believed to be a Nuchequula species, whereas L. ruconius (NC 057225) is not classified under Leiognathus in the NCBI database. The phylogenetic trees divided the Leiognathidae family into three clades. The mitogenome phylogeny suggested that the Leiognathidae and Chaetodontidae clades are sister groups. These findings provide important genetic data for population genetics research and a phylogenetic analysis of Leiognathidae.

The ponyfish genus Aurigequula is a relatively poorly studied group within the Leiognathidae, with its diversity and phylogenetic relationships in the West Pacific remaining unclear. This study reports the first confirmed record of Aurigequula striata from Chinese waters, based on two specimens obtained from a fish market in Sanya, Hainan Island. Newly collected specimens of A. fasciata from the same region are also provided, which enabled detailed morphological and genomic analysis. The morphological descriptions are supplemented by detailed photographic documentation of fresh and preserved specimens, addressing the historical scarcity of reliable visual references for these species. Furthermore, we present the first complete mitochondrial genomes for both A. striata (16,629 bp) and A. fasciata (16,537 bp). Our phylogenomic analysis, based on 13 protein-coding genes, strongly supports the monophyly of the subfamilies Gazzinae and Leiognathinae. Within Leiognathinae, however, the analysis suggests paraphyly of Aurigequula , with A. fasciata forming a clade with Leiognathus equula to the exclusion of A. striata . This result conflicts with the current morphology-based generic diagnosis, which relies on consistent differences in the length of the second dorsal-fin spine and body coloration patterns. This study significantly expands the genomic resources for the understudied genus Aurigequula but also highlights the limitations of relying solely on mitochondrial data for resolving generic-level relationships. A more robust phylogenetic framework for Leiognathidae, capable of reconciling molecular and morphological evidence, will require the integration of multiple independent nuclear loci.

During our investigation of the diversity and phylogeny of the family Semisulcospiridae in China, we have found a presumed new species in mountain streams of Xiamen, Fujian Province on both morphology and molecular evidence. This new species, Semisulcospira egrettasp. nov., is characterized by its thin and smooth shell, retaining about 0.5 mm long embryonic shells in its brood pouch, and by distinctive features of its radular morphology. Phylogenetic analyses of partial sequences of the mitochondrial markers 16S ribosomal RNA (16S) and cytochrome c oxidase subunit I (COI) and complete sequences of the nuclear ribosomal internal transcribed spacer (ITS, including internal transcribed spacer 1, 5.8S ribosomal RNA gene, and internal transcribed spacer 2) supported the distinctiveness of S. egrettasp. nov. from other Semisulcospira species. These analyses consistently placed S. egrettasp. nov. in Semisulcospira confirming its monophyly. Phylogenetic analyses based on just COI and 16S exhibited low resolution rendering the phylogenetic position of the new species within the genus uncertain. In contrast, phylogenetic tree analyses of complete mitochondrial genomes, which include 13 protein-coding genes (PCGs), were better resolved. However, the mitogenome dataset included a more restricted sampling of taxa (16), impeding a detailed exploration of the phylogenetic position of the new species. To address this deficit, we provide seven complete mitochondrial genomes for S. egrettasp. nov., obtained using the genome skimming sequencing method. This study contributes important molecular and genomic data, aiding in the understanding of semisulcospirid phylogeny, and highlights the need for further taxonomic sampling and phylogenomic methods to resolve the evolutionary relationships within Semisulcospiridae.

Podarkeopsis chinensissp. nov. (Annelida, Hesionidae) is described based on specimens collected from the coast of southeast China. It is the first Podarkeopsis species described from the Indo-Pacific, although there are already nine valid Podarkeopsis species known from other parts of the world. This new species can be distinguished from the other Podarkeopsis species in having a palpostyle as long as the palpophore and double aciculae in both notopodia and neuropodia, and in bearing bifid furcate chaetae which have a smooth base on the shorter tine. A phylogenetic analysis based on the concatenated sequences of five gene fragments (COI, 16S rRNA, 18S rRNA, 28S rRNA, and histone H3) from 18 specimens of P. chinensissp. nov. showed that they formed a monophyletic clade that is sister to P. levifuscina. K2P genetic distances indicated that the four gene fragments (COI, 16S rRNA, 18S rRNA, and 28S rRNA) of P. chinensissp. nov. diverged from the corresponding sequences of the closest related species of Podarkeopsis in GenBank and BOLD Systems by 21.1–27.5%, 20.3–23.1%, 0.1–0.2%, and 2.1–3.2%. An identification key is provided for species in the genus Podarkeopsis.