The mitochondrial genome (mitogenome) can provide information for phylogenetic analyses and evolutionary biology. We first sequenced, annotated, and characterized the mitogenome of Philomycus bilineatus in this study. The complete mitogenome was 14,347 bp in length, containing 13 protein-coding genes (PCGs), 23 transfer RNA genes, two ribosomal RNA genes, and two non-coding regions (A + T-rich region). There were 15 overlap locations and 18 intergenic spacer regions found throughout the mitogenome of P. bilineatus. The A + T content in the mitogenome was 72.11%. All PCGs used a standard ATN as a start codon, with the exception of cytochrome c oxidase 1 (cox1) and ATP synthase F0 subunit 8 (atp8) with TTG and GTG. Additionally, TAA or TAG was identified as the typical stop codon. All transfer RNA (tRNA) genes had a typical clover-leaf structure, except for trnS1 (AGC), trnS2 (TCA), and trnK (TTT). A phylogenetic analysis with another 37 species of gastropods was performed using Bayesian inference, based on the amino acid sequences of 13 mitochondrial PCGs. The results indicated that P. bilineatus shares a close ancestry with Meghimatium bilineatum. It seems more appropriate to reclassify it as Arionoidea rather than Limacoidea, as previously thought. Our research may provide a new meaningful insight into the evolution of P. bilineatus.

Background: Luciocyprinus langsoni is a species belonging to the Cyprinidae family. The objective of this study is to gain a comprehensive understanding of its evolutionary history and genetic characteristics. Methods: The complete mitochondrial genome of L. langsoni was determined using overlapping PCR. A phylogenetic analysis was conducted based on 13 protein-coding genes from 48 species. A population genetic diversity analysis using the COI gene and a selection analysis of 13 protein-coding genes were also performed. Results: The mitogenome is 16,586 base pairs long and consists of 13 protein-coding genes, two ribosomal RNAs, 22 transfer RNAs, and two control regions. It has a high adenine-thymine (A + T) content. The phylogenetic analysis confirms the placement of L. langsoni within the subfamily Cyprininae. The population genetic diversity analysis reveals low variability in the Hechi Longjiang population. The selection analysis shows that all 13 protein-coding genes have evolved under purifying selection with Ka/Ks ratios below 1. Conclusions: These results enhance our understanding of L. langsoni’s evolutionary history and lay a genetic foundation for future studies in population genetics and phylogenetics.

The sea slug Onchidium reevesii inhabits the intertidal zone, which is characterized by a changeable environment. Although the circadian modulation of long-term memory (LTM) is well documented, the interaction of the circadian clock with light–dark masking in LTM of intertidal animals is not well understood. We characterized the LTM of Onchidium and tested the expression levels of related genes under a light–dark (LD) cycle and constant darkness (i.e., dark–dark, or DD) cycle. Results indicated that both learning behavior and LTM show differences between circadian time (CT) 10 and zeitgeber time (ZT) 10. In LD, the cry1 gene expressed irregularly, and per2 expression displayed a daily pattern and a peak expression level at ZT 18. OnCREB1 (only in LD conditions) and per2 transcripts cycled in phase with each other. In DD, the cry1 gene had its peak expression at CT 10, and per2 expressed its peak level at CT 18. OnCREB1 had two peak expression levels at ZT 10 or ZT 18 which correspond to the time node of peaks in cry1 and per2, respectively. The obtained results provide an LTM pattern that is different from other model species of the intertidal zone. We conclude that the daily transcriptional oscillations of Onchidium for LTM were affected by circadian rhythms and LD cycle masking.

In the present study, we have sequenced, annotated and characterized the complete mitogenome of Tanichthys flavianalis Li, Liao & Shen, 2022, which is an endemic minnow to Hainan Province, China. The entire mitogenome size is 16,545 bp, containing 37 genes coding for 13 mitochondrial proteins, 22 tRNAs, 2 rRNAs, and one putative control region. It has the typical fish mitochondrial gene arrangement, though with 9 gene overlaps and 17 intergenic spacers scattering throughout the mitogenome, and a high A + T bias (60.8%) comparing to other Cyprinids. ATG is used as the start codon in most mitochondrial protein coding genes (PCGs) except for cox1 which uses GTG, whereas the canonical TAA/TAG are prevailing stop codons except for cox2, cox3, nad4 and cytb. Phylogenetic analyses with other reported species from Tanichyidae were conducted using IQ-TREE and MrBayes, based on the concatenated 13 PCGs. The results clustered T. flavinalis with the newly described T. albiventris Li Bohlen & Liao, 2022, and proved the reciprocally monophyletic relationship between Chinese and Vietnamese Tanichthys.

Background/Objectives: Liobagrus huaiheensis, an endemic fish in the Huaihe River basin, is a newly described species with limited molecular genetic research, hindering understanding of its evolutionary status, population structure, and genetic diversity. This study aimed to characterize its complete mitochondrial genome, clarify its phylogenetic position within Liobagrus, and assess its population genetic diversity. Methods: We obtained the complete mitogenome of L. huaiheensis (sourced from the Zhugan River) through sequencing, followed by detailed annotation of this genomic sequence. We analyzed its genomic structure, nucleotide composition, codon usage, and base asymmetry. Selection pressure on 13 protein-coding genes (PCGs) was evaluated using Ka/Ks ratios. Phylogenetic trees were generated by means of Bayesian inference (BI) and maximum likelihood (ML), using a dataset composed of 13 protein-coding genes (PCGs) from 37 species. Population genetic diversity was assessed using the cox1 gene. Results: The mitogenome is a 16,512 bp circular molecule encoding 37 genes and one control region, with a conserved structure typical of Liobagrus. It has high A + T content (55.74%) with A-preference and C-enrichment. All PCGs undergo purifying selection (Ka/Ks < 1). Phylogenetic analyses revealed L. huaiheensis is closest to L. obesus (100% support), with Liobagrus divided into three clades. The cox1 gene analysis showed low diversity (Hd = 0.656, π = 0.00171) and neutral evolution. Conclusions: This study fills the mitogenome data gap for L. huaiheensis, clarifies its evolutionary characteristics and phylogenetic position, and provides a basis for conservation genetics of Huaihe endemic fishes and molecular evolution research on Amblycipitidae.