Littoraria melanostoma (Gray, 1839) is one of the most common species of gastropods in mangroves. They quickly respond during the early stage of mangrove restoration and usually form a dominant community within a certain period. We characterized the complete mitochondrial genome of this species. The whole mitogenome of L. melanostoma was 16,149 bp in length and its nucleotide composition showed a high AT content of 64.16%. It had 37 genes, including 13 protein-coding genes, 2 ribosomal RNA genes, and 22 transfer RNA genes, and 1 control region between tRNA-Phe and COX3. The A/T composition in the control region was 74.7%, and is much higher than the overall A/T composition of the mitochondrial genomes. The amino acid composition and codon usage of the mitochondrial genomes from seven superfamilies of Littorinimorpha were analyzed, and the results showed that CUU (Leu), GCU (Ala), AUU (Ile), UCU (Ser), UUA (Leu), GUU (Gly), and UUU (Phe) are the commonly used codons. The maximum likelihood phylogenetic tree reconstructed using 62 species of Littorinimorpha presented consistency between the molecular and morphological classifications, which provide a basis to understand the phylogeny and evolution of this order. In the phylogenetic tree, L. melanostoma is located within Littorinoidea and is closely related to L. sinensis, a rock-dwelling species that is widespread in the coastal intertidal zone of China.

Geloina erosa is an important benthic animal in the mangrove, serving as an indicator organism for coastal environmental pollution. This study aimed to investigate the tissue-specific expression of miRNAs and their regulatory roles in predicted targets in G. erosa. Through miRNA sequencing and co-expression network analysis, we extensively studied the miRNA expression in three tissues: gills, hepatopancreas, and muscle. The results revealed a total of 1412 miRNAs, comprising 1047 known miRNAs, and 365 newly predicted miRNAs. These miRNAs exhibited distinct tissue-specific expression patterns. In the miRNA target gene prediction, a total of 7404 potential predicted targets were identified, representing approximately 33% of all unique transcripts associated with miRNAs. Further co-expression network analysis revealed nine modules, each showing a positive correlation with specific tissues (gills, hepatopancreas, or muscle). The blue module showed a significant correlation with gills (r = 0.83, p-value = 0.006), the black module was significantly related to the hepatopancreas (r = 0.78, p-value = 0.01), and the purple module was significantly correlated with muscle (r = 0.83, p-value = 0.006). Within these modules, related miRNAs tended to cluster together, while their correlations with other modules were relatively weak. Functional enrichment analysis was performed on miRNAs and their predicted targets in each tissue. In the gills, miRNAs primarily regulate immune-related genes, substance transport, and cytoskeletal organization. In the hepatopancreas, miRNAs suppressed genes involved in shell formation and played a role in cellular motor activity and metabolism. In muscle, miRNAs participate in metabolism and photoreceptive processes, as well as immune regulation. In summary, this study provides valuable insights into the tissue-specific regulation of miRNAs in G. erosa, highlighting their potential roles in immune response, metabolism, and environmental adaptation. These findings offer important clues for understanding the molecular mechanisms and biological processes in G. erosa, laying the foundation for further validation and elucidation of these regulatory relationships.

Littoraria melanostoma (Gray, 1839) is a most common species of gastropods in mangroves. They quickly respond during the early stage of mangrove restoration and usually form a dominant community within a certain period. We characterized the complete mitochondrial genome of the species. The whole mitogenome of L. melanostoma was 16,149 bp in length and its nucleotide composition showed high AT-content of 64.16%. It had 37 genes, including 13 protein-coding genes, two ribosomal RNA genes, and 22 transfer RNA genes, one control region between tRNA-Phe and COX3. The A/T compositions in the control region is 74.7%, respectively, and are much higher than the overall A/T composition of the mitochondrial genomes. The amino acid composition and codon usage of the mitochondrial genomes of from eight superfamilies of Littorinimorpha were analyzed, and the results showed that CUU (Leu), GCU (Ala), AUU (Ile), UCU (Ser), UUA (Leu), GUU (Gly) and UUU (Phe) are the commonly used codons in this order. The results of phylogenetic analysis were roughly consistent with morphological classification, which showed that L. melanostoma is closely related to L. sinensis, a rock-dwelling species that is widespread in the coastal intertidal zone of China. These results may provide a basis to understand the phylogeny and evolution of the Littorinimorpha.