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Heterosigma akashiwo is a harmful algal bloom species that causes significant detrimental effects on marine ecosystems worldwide. The algicidal bacterium Pseudalteromonas sp. LD-B1 has demonstrated potential effectiveness in mitigating these blooms. However, the molecular mechanisms underlying LD-B1’s inhibitory effects on H. akashiwo remain poorly understood. In this study, we employed the comprehensive methodology, including morphological observation, assessment of photosynthetic efficiency (Fv/Fm), and transcriptomic analysis, to investigate the response of H. akashiwo to LD-B1. Exposure to LD-B1 resulted in a rapid decline of H. akashiwo's Fv/Fm ratio, with cells transitioning to a rounded shape within 2 hours, subsequently undergoing structural collapse and cytoplasmic leakage. Transcriptomic data revealed sustained downregulation of photosynthetic genes, indicating impaired functionality of the photosynthetic system. Additionally, genes related to the respiratory electron transfer chain and antioxidant defenses were consistently downregulated, suggesting prolonged oxidative stress beyond the cellular antioxidative capacity. Notably, upregulation of autophagy-related genes was observed, indicating autophagic responses in the algal cells. This study elucidates the molecular basis of LD-B1's algicidal effects on H. akashiwo, advancing our understanding of algicidal mechanisms and contributing to the development of effective strategies for controlling harmful algal blooms.

AbstractBarnacles are crustaceans that are critical model organisms in intertidal ecology and biofouling research. In this study, we present the first mitochondrial genome of Striatobalanus tenuis which is a circular molecule of 15,067 bp in length. Consistent with most barnacles, the mitochondrial genome of S. tenuis encodes 37 genes, including 13 PCGs, 22 tRNAs and 2 rRNAs. A novel insight into the phylogenetic analysis based on the nucleotide data of 13 PCGs showed that the S. tenuis clusters with Striatobalanus amaryllis (bootstrap value = 100) of the same genus, then groups with other Balanoidea species, the Chelonibiidae, Austrobalanidae and Tetraclitidae cluster together forming superfamily Coronuloidea. The result can help us to understand the novel classification within Balanomorpha.

Barnacles have demonstrated adaptability to a range of habitats, spanning from shallow water to the deep sea. Given the harsh conditions present in hydrothermal vents, hydrothermal vent barnacles serve as the model organism for investigating the interplay between evolution and adaptability. In order to gain insights into barnacle adaptive characteristics, particularly within hydrothermal vents, we conducted a comprehensive analysis of the mitogenomes and transcriptome in a deep-sea barnacle (Neolepas marisindica), in comparison to its shallow-water related species. The mitogenomes with the same genetic skews and the non-synonymous/synonymous mutation ratios (Ka/Ks) of the mitogenomes indicate that the protein-coding genes (COIII, ND2, and ND6) of N. marisindica are under positive selection. Meanwhile, the functional annotation shows that distinctly positive selected orthologs in N. marisindica are predominately related to neural signal transduction, immunity, antiapoptotic, and energy metabolism. These results indicate that the mitogenomes and key genes found in transcriptomic analysis are under high-temperature and high-pressure conditions, and which may contribute N. marisindica to have evolved to adapt to the extreme hydrothermal vent environments. The findings shed light on the mitogenome and transcriptome of N. marisindica, which lays a foundation for the in-depth understanding of the adaptation mechanism of sessile invertebrates to the deep-sea environment.

IntroductionThe deep-sea environment is always characterized by high hydrostatic pressure, fluctuating temperatures, heavy metals, darkness, and others. The Vesicomyidae inhabit cold seep zones, hydrothermal vents, and other chemically reduced environments.MethodsTo enhance the understanding of the adaptation mechanisms of clams in extreme environments, a comprehensive proteomic study was conducted on the cold seep clam Archivesica marissinica and shallow water clam Ruditapes philippinarum.ResultsA total of 4,557 proteins were identified from the comparative groups. The Gene Ontology results indicated that the differentially expressed proteins (DEP) for the comparative group Rpgill vs. Amgill were enriched in the nitrogen compound metabolic process, and others. The comparative analysis for Amfoot vs. Amgill and Ammantle vs. Amgill revealed significant enrichment of the differential proteins that were involved in metal ion transport, divalent inorganic cation transport, and so on. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis for the comparative group Rpgill vs. Amgill was significantly enriched in the regulation of actin cytoskeleton, lysosome, and others. The proteins that exhibited differential expression in the cold seep clam’ different tissues were also enriched in important pathways, such as lysosome, fatty acid degradation, nitrogen metabolism.DiscussionThe further analysis identified crucial response proteins involved in various biological pathways. For example, the pattern recognition receptors, such as galectin and peptidoglycan recognition protein, participated in recognition of symbiotic microorganisms. The lysosome pathway members, such as cathepsin and saposins, were engaged in the degradation process of symbiont proteins during symbiont digestion. Profilin and gelsolin from actin cytoskeleton pathway might be pressure-related proteins. Furthermore, carbonic anhydrases from nitrogen metabolism KEGG pathway provide inorganic carbon for symbiotic bacteria. Additionally, Mn superoxide dismutase plays a role in the scavenging of superoxide anion radicals and antioxidant activity. Then, arginine kinases facilitate the low temperature adaptation of deep-sea shellfish with its cold adaptation characters. These findings offer novel perspectives on the proteins that are implicated in A. marisica’s response to cold seep environments, thereby contributing to the understanding of deep-sea biological adaptation and the preservation of deep-sea ecosystems.

The dinoflagellate Noctiluca scintillans is a globally distributed bloom-forming species. Previous studies have shown that the primary reason for the frequent occurrence of N. scintillans blooms may be the proliferation of microalgae due to eutrophication, which provides a sufficient source of food. Meanwhile, N. scintillans may release nutrients into the environment, thus affecting the population dynamics of microalgae. Thus, to investigate the interaction between N. scintillans and co-occurring microalgae, this study examined the population dynamics of N. scintillans and their interaction with three representative microalgae species in response to varying nutrient levels. The findings indicate that the growth of N. scintillans is slow when co-cultured with diatom Skeletonema costatum. Moreover, a high density and rapid growth rate of S. costatum may have an inhibitory effect on the growth of N. scintillans. Conversely, the population abundance of N. scintillans increased with the rise in the population density and nutritional level of Heterocapsa steinii (dinoflagellate) and Heterosigma akashiwo (raphidophyceae). Notably, N. scintillans can discharge specific nutrients into the aquatic environment, which can subsequently be assimilated and exploited by H. steinii. Thus, the interaction between the species and population dynamics of plankton, as well as changes in nutrient levels within the ecosystem, played a significant role in influencing the growth and population dynamics of N. scintillans. The mutualistic association between N. scintillans and microalgae may establish a transient closed loop, thereby fostering the sustained proliferation and subsequent expansion of N. scintillans.

The receptor for activated protein kinase C1 (RACK1) belongs to the typical WD repeat family, which is extremely conservative and important in multiple signal transduction pathways related to growth and development that coordinate the intracellular role of various life activities. As a novel protein with versatile functions, it was found in a variety of organisms. In a previous study, we identified the RACK1 sequence of white shrimp from transcriptome data. In this study, we employed specialized bioinformatics software to conduct an in-depth analysis of EcRACK1 and compare its amino acid sequence homology with other crustaceans. Furthermore, we investigated the expression patterns of RACK1 at different developmental stages and tissues, as well as at various time points after exposure to Aroclor 1245, aiming to elucidate its function and potential response towards Aroclor 1245 exposure. The length of EcRACK1 is 957 nucleotides, which encodes 318 amino acids. Moreover, there were seven typical WD repeats in EcRACK1, which have more than a 96% sequence identity with the RACK1 proteins of Penaeus. The results of tissue expression and spatiotemporal expression showed that it was significantly increased in the II and IV stages, but had a significant tissue specificity in the hepatopancreas, spermary, and muscle tissues of E. carinicauda, adult stage. Compared to the control, EcRACK1 was significantly induced in E. carinicauda zoea larvae exposed to Aroclor 1254 for 6, 10, 20, and 30 d (p < 0.05). These results suggested that EcRACK1 may play an important role in the larval development and environmental defense of E. carinicauda.

Florfenicol (FLR), a broad-spectrum antibacterial agent, is commonly used in the breeding and cultivation of aquatic animals. microRNAs (miRNAs) control gene expression by mediating post-transcriptional mRNA repression. However, not much has been reported regarding their functions when crustaceans encounter FLR stress. Herein we observed histological alterations and performed small RNA sequencing to characterize differentially expressed miRNAs in the hepatopancreas of Portunus trituberculatus exposed to FLR (80 mg/kg) stress for 3 h and 12 h. Our results indicated irregularities in the tubular structure of hepatopancreas, separation between epithelium and myoepithelial layer, ruptured epithelial cells, and tubule degeneration. Thirty-five (19 up- and 16 downregulated) and 31 (17 up- and 14 downregulated) differentially expressed miRNAs were detected between Group-C and Group-FLR-3 h and between Group-C and Group-FLR-12 h, respectively. Dual luciferase reporter assay was performed for predicting target genes of miR-34 and miR-263b. We found that mir-263b directly inhibited cytochrome C expression at the cell level in vitro. Functional analyses of predicted target genes of differentially expressed miRNAs revealed that FLR stress induced xenobiotic metabolism, immune toxicity, and cell apoptosis, as well as influenced diverse metabolic processes. To our knowledge, this is the first report on the response of P. trituberculatus to FLR stress. Our findings provide evidence that miRNAs participate in cell apoptosis and immune regulation in crabs.

The dinoflagellate Noctiluca scintillans is a harmful algal species that is globally distributed and poses a certain threat to marine ecosystems. Recent research has shown that the application of algicidal bacteria is a promising method to prevent and control such harmful algal blooms (HABs), given its advantages of safety and efficiency. In this study, a strain of algicidal bacterium LD-B6 with high efficiency against N. scintillans was isolated from the coastal waters of Lianyungang, China. 16S rDNA sequence analysis showed that the strain LD-B6 belongs to the genus Pseudoalteromonas. Furthermore, the algicidal effect of LD-B6 on N. scintillans was investigated. The results showed that strain LD-B6 exerted strong algicidal activity against N. scintillans. After 12 h of bacterial culture addition to algal cultures at a 2% final volume rate, the algicidal activity reached 90.5%, and the algicidal activity of LD-B6 was influenced by the density of N. scintillans. In addition, the algicidal bacterium LD-B6 was found to indirectly lyse algal cells by secreting extracellular compounds. These algicidal compounds were stable, indicating that they are not proteins. Importantly, strain LD-B6 was broadly general, showing varying degrees of lysing effects against five of the six algal species tested. On the basis of the described studies above, the algicidal powder was also initially developed. In summary, the isolated bacterial strain LD-B6 shows the potent algicidal capability to serve as a candidate algicidal bacterium against N. scintillans blooms.

The raphidophyte Heterosigma akashiwo is a harmful algal species. The bloom of this organism has been associated with the massive mortality of fish in many coastal waters. To investigate the molecular mechanism of H. akashiwo blooms, having a reliable reference transcriptome of this species is essential. Therefore, in this study, a full-length transcriptome of H. akashiwo was obtained by single-molecule real-time sequencing. In total, 45.44 Gb subread bases were generated, and 16,668 unigenes were obtained after the sequencing data processing. A total of 8666 (52.00%) unigenes were successfully annotated using seven public databases. Among them, mostly phosphorus and nitrogen metabolism genes were detected. Moreover, there were 300 putative transcription factors, 4392 putative long non-coding RNAs, and 7851 simple sequence repeats predicted. This study provides a valuable reference transcriptome for understanding how H. akashiwo blooms at a molecular level.

The ichthyotoxic raphidophyte Heterosigma akashiwo is associated with harmful algal blooms (HABs). Although the influence of H. akashiwo on fish has been reported, little is known of its effects on other marine organisms, such as shellfish. In this study, the physiological and transcriptomic responses of the Asiatic hard clam Meretrix meretrix to H. akashiwo were investigated. The results showed that clam survival was not influenced by H. akashiwo (at a concentration of 2 × 104 cells/mL), and M. meretrix eliminated the alga effectively after 48 h in co-culture. H. akashiwo did not alter the antioxidant capacity of the clams. However, 544 unigenes were found to be differentially expressed between the control and H. akashiwo-treated clams. Interestingly, the significant up-regulation of lysosome-related genes and transport proteins suggested remodeling of the clam metabolism possibly for digestion of H. akashiwo. In summary, our results indicate that the clam M. meretrix can effectively feed on H. akashiwo, and intensification of shellfish farming may be helpful to control and mitigate H. akashiwo blooms.

Megabalanus coccopoma (Darwin, 1854) is a globally invasive species in Balanomorpha (Crustacea). This species is a model organism for studying marine pollution and ecology. However, its mitogenome remains unknown. The mitogenome sequencing of M. coccopoma is completed in the present study. It has a 15,098 bp in length, including 13 protein-coding genes (PCGs), 2 ribosomal RNAs (rRNAs), 22 transfer RNAs (tRNAs), along with a putative regulatory area. A substantial A+T bias was observed in the genome composition (68.2%), along with a negative AT (0.82) and GC (−0.136) skew. Compared to the gene sequence of the ground model of pan-crustacea, 13 gene clusters (or genes), such as 10 tRNAs and 3 PCGs, were observed in a different order. This was in line with the previously observed large-scale gene rearrangements of Balanomorpha. Among the 37 genes, the gene cluster (M-nad2-W-cox1-L2-cox2-D-atp8-atp6-cox3-G- nad3-R-N-A-E-S1) Balanomorpha was conserved. Furthermore, phylogeny analysis indicated that the existing Balanomorpha species family was divided into nine rearrangement patterns, supporting the polyphyly of Balanoidea.

The triangle barnacle Balanus trigonus Darwin, 1854, a cosmopolitan inhabitant of tropical and warm temperate seas, is a member of robust system for the study of evolutionary processes in the intertidal zone. The first mitochondrial genome of B. trigonus is presented. The complete mitochondrial genome of B. trigonus is a circular molecule of 15,560 bp, which encodes 13 protein-coding genes (PCGs), 2 rRNA genes, and 22 tRNA genes. In comparison within Sessilia, the arrangement of the mitochondrial genome of B. trigonus is more similar to Megabalanus spp. than the congener Balanus balanus, which share a same inversion of a large gene block (P-nd4L-nd4-H-nd5-F). Phylogenetic analysis based on mitochondrial PCGs reveals that B. trigonus clusters with Acasta Sulcata (BP = 100), then grouped with Megabalanus volcano and Megabalanus ajax with high support (BP = 90). In further, more data and research are needed to reveal the phylogeny within Cirripedia.

The complete mitochondrial genome of Tetraclita japonica (Crustacea: Maxillopoda: Sessilia) from Zhejiang (China) was presented (T. japonica ZJ). The genome is a circular molecule of 15,192 bp, all non-coding regions are 694 bp in length, and the longest one (307 bp) is located between 12S rRNA and trnK. Phylogenetic analysis based on mitochondrial PCGs shows that T. japonica ZJ clusters with T. japonica CN, and they grouped with T. japonica (BP = 100), then grouped with Tesseropora rosea, Tetraclita serrata, Tetraclita rufotincta, Epopella plicata, and Tetraclitella divisa successively . The phylogenetic tree indicated that the Balanidae and Archaeobalanidae are polyphyletic, while the Chthamalidae is monophyletic. The result can help us to understand the phylogenetic history within Sessilia.

The first complete mitochondrial genome of the intertidal barnacle Fistulobalanus albicostatus Pilsbry, 1916 (Crustacea: Maxillopoda: Sessilia) is presented. The genome is a circular molecule of 15,665 bp, which encodes a set of 37 typical metazoan genes. All non-coding regions are 438 bp in length, with the longest one speculated as the control region (264 bp), which is located between srRNA and trnI. All protein-coding genes (PCGs) have an ATD (ATA, ATT, or ATG) start codon, except nad1, which is initiated with GTG. Remarkably, cox3, cob, nad1-5 have incomplete stop codons (T–– or TA–) and the remaining PCGs have the complete stop codon (TAA). Phylogenetic analysis based on 13 mitochondrial PCGs shows that the members of the Archaeobalanidae and Balanidae intermingle with species from Pyrgomatidae. The results supposed that Balanidae and Archaeobalanidae are non-monophyly.

Polychlorinated biphenyls (PCBs) are well-known persistent organic pollutants; they have toxic effects on the immune system, reproductive system, and endocrine system by changing the metabolism of the body. To elucidate the underlying molecular mechanism, the clam Meretrix meretrix was exposed to 10 and 1000 ng/L Aroclor 1254 and natural seawater (control). Samples from clams exposed to natural seawater and those exposed to Aroclor 1254 for 1 and 3 days were individually collected for transcriptome analysis. After assembly, more than 535,157 transcripts with a mean length of 949 bp and an N50 length of 1279 bp were obtained; a final set of 177,142 unigenes was generated. In the present study, 5101 differentially expressed genes were identified. The differentially expressed genes were related to detoxification metabolism, oxidative stress, immune response, and endocrine system disruption. Of these genes, under the Aroclor 1254 exposure, cytochrome P450 20A1 (2.06–4.46 folds), glutathione S-transferase (2.25–3.80 folds), multidrug resistance-associated protein 1-like (1.49–2.92 folds), peroxidase-like protein (1.33–4.26 folds), lysozyme (1.61–2.05 folds), bcl-2 like 1 protein (1.14–2.29 folds) and vitellogenin (1.09–1.19 folds) showed been significantly induced expressed. At the same time, some genes were down regulated, including cytochrome P450 2J5 (−1.20 ~ −2.86 folds), cytochrome P450 3A24 (−1.40 ~ −4.08 folds), C1q (−1.27 ~ −1.66 folds), Sulfotransferase (−1.51 ~ −1.84 folds), monocarboxylate transporter 10 (−1.30 ~ −4.70 folds), 3-beta hydroxysteroid dehydrogenase (−1.43 ~ −2.81 folds) and beta-galactosidase (−1.23 ~ −2.23 folds). Furthermore, it showed that the expression levels of CYP2J5, glutathione S-transferase, 3-beta hydroxysteroid dehydrogenase and beta-galactosidase had time responses and dose responses. The present study provided insights into the toxic effects of Aroclor 1254 exposure in M. meretrix.

The first mitochondrial genome of Tetraclita japonica from China was presented. The mitochondrial genome of T. japonica CN is a circular DNA molecule containing 15,192 bp. It contains 13 protein-coding genes, two rRNAs genes and 22 tRNAs. Four PCGs, seven tRNAs, and two rRNAs are encoded on the light strand (trnF, nd5, trnH, nd4, nd4L, trnP, nd1, trnL1, lrRNA, trnV, srRNA, trnK, and trnQ), and the other nine PCGs are located on the heavy strand. The length of all non-coding regions is 667 bp and the longest one distributed between srRNA and trnK (263 bp). Interestingly, cox1 of T. japonica CN started with CGA, which is different from most other mitochondrial PCGs whose initiation codon is ATN. In comparison with the pancrustacean ground pattern, seven tRNAs (trnQ, trnI, trnP, trnT, trnS1, trnE, and trnA) are translocated, and three tRNAs (trnK, trnC, and trnY) are inverted. Phylogenetic tree was constructed based on 13 mitochondrial PCGs. In the phylogenetic tree, T. japonica CN clustered with T. japonica JP into a branch (BP = 100). Tesseropora rosea clustered with T. japonica, and they grouped with T. rufotincta with high support (BP = 100). In the tree, T. divisa as the most distantly related species within Tetraclitidae. Moreover, phylogenetic analysis indicates that the two families (Balanidae and Archaeobalanidae) are non-monophyletic. More mitochondrial genomic data are urgently needed to reveal the deeper phylogeny within Cirripedia.

Macrobrachium rosenbergii de Man, 1879 (Caridea: Palaemonidae), commonly referred to as giant freshwater prawn, is commercially important worldwide, and a primary inland cultured species. The first complete mitochondrial genome of M. rosenbergii from China (CN) was sequenced and compared with that in Indonesia (ID) in this study. The results show that the total length of CN-mtDNA sequence is 15,767 bp (GenBank accession number: KY865098), which is shorter than that of ID-mtDNA (15,772 bp). It encodes 37 genes, including 13 protein-coding genes, 22 transfer RNA genes and 2 ribosomal RNA genes. The heavy strand and light strand encode 23 and 14 genes, respectively, and the content of A + T is 61.81%. The gene order and content of CN-mtDNA and ID-mtDNA are identical to the primitive Pancrustacean ground pattern. Phylogenetic analysis shows that CN-mtDNA is clustered into one clade with ID-mtDNA (BP =100). Pairwise genetic distance analyses indicate that the genetic distance of CN-mtDNA and ID-mtDNA is 0.086, which is smaller than values between species in the Macrobrachium genus. In summary, both phylogenetic analysis and gene re-arrrangement analysis between the M. rosenbergii in China and Indonesia have revealed that their differences are within intraspecific variation.

We determined the first mitochondrial genome of Tetraclita kuroshioensis from China. The mitochondrial genome of T. kuroshioensis was found to be 15,175 bp in length and consisted of 13 protein-coding genes (PCGs), 22 tRNAs, and 2 rRNAs. The longest non-coding region was 425 bp in length. Phylogenetic analysis showed that T. kuroshioensis clustered with T. serrata and then clustered with T. squamosa squamosa with high bootstrap value (BP = 100). In the future, sequencing of additional mitochondrial genomes should provide additional insights into the deep phylogeny of Cirripedia.

Cirripedia is a lower crustacean that has an invaluable place in several aspects of intertidal ecology and anti-fouling research. In this study, we present the first mitochondrial genome of Chthamalus malayensis. The complete mitochondrial genome of C. malayensis is a circular molecule of 15,230 bp. In comparison to the pancrustacean ground pattern, the mitochondrial genome of C. malayensis has a deletion of the trnC gene. Phylogenetic analysis based on mitochondrial protein-coding genes showed that C. malayensis clusters with C. antennatus (BP = 98) and is grouped with C. challengeri, Octomeris sp. BKKC-2014, and Notochthamalus scabrosus. Further studies are needed to reveal the specific phylogenic relationships within Cirripedia.

The complete mitochondrial genome of Glycera chirori Izuka (Annelida: Polychaeta) was presented, which is a circular molecule of 15,930 bp nucleotides. It encodes 37 genes, including 13 PCGs, 22 tRNAs, and two rRNAs. The length of non-coding regions is 1428 bp, and the longest one (1346 bp) is speculated as the control region, which is located between trnA and trnL2 and is longer than most species in Glycera. The complete mitogenome of G. chirori Izuka consists of 31.2% A, 23.6% C, 12.9% G, and 32.2% T, which has T vs. A skew (−0.02) and C vs. G skew (−0.29), respectively. Phylogenetic analysis indicates the classification status of G. chirori Izuka and the relationship with other species in Glycera, which is closer with Glycera unicornis and Glycera fallax (bootstrap = 100). By comparisons, the gene arrangement of G. chirori Izuka and other seven species in Glycera are identical and they also cluster together in phylogenetic tree with higher support rate, which indicates the conservativeness between gene arrangement and phylogenetic analysis in Glycera. In conclusion, the complete mitochondrial genome of G. chirori Izuka can provide supportive data for further molecular and evolutionary analysis of Glycera.

Barnacles have demonstrated adaptability to a range of habitats, spanning from shallow water to the deep sea. Given the harsh conditions present in hydrothermal vents, hydrothermal vent barnacles serve as the model organism for investigating the interplay between evolution and adaptability. In order to gain insights into barnacle adaptive characteristics, particularly within hydrothermal vents, we conducted a comprehensive analysis of the mitogenomes and transcriptome in a deep-sea barnacle (Neolepas marisindica), in comparison to its shallow-water related species. The mitogenomes with the same genetic skews and the non-synonymous/synonymous mutation ratios (Ka/Ks) of the mitogenomes indicate that the protein-coding genes (COIII, ND2, and ND6) of N. marisindica are under positive selection. Meanwhile, the functional annotation shows that distinctly positive selected orthologs in N. marisindica are predominately related to neural signal transduction, immunity, antiapoptotic, and energy metabolism. These results indicate that the mitogenomes and key genes found in transcriptomic analysis are under high-temperature and highpressure conditions, and which may contribute N. marisindica to have evolved to adapt to the extreme hydrothermal vent environments. The findings shed light on the mitogenome and transcriptome of N. marisindica, which lays a foundation for the in-depth understanding of the adaptation mechanism of sessile invertebrates to the deep-sea environment. [ABSTRACT FROM AUTHOR]

Barnacles have demonstrated adaptability to a range of habitats, spanning from shallow water to the deep sea. Given the harsh conditions present in hydrothermal vents, hydrothermal vent barnacles serve as the model organism for investigating the interplay between evolution and adaptability. In order to gain insights into barnacle adaptive characteristics, particularly within hydrothermal vents, we conducted a comprehensive analysis of the mitogenomes and transcriptome in a deep-sea barnacle (Vulcanolepas fijiensis), in comparison to its shallow-water related species. The mitogenomes with the same genetic skews and the non-synonymous/synonymous mutation ratios (Ka/Ks) of the mitogenomes indicate that the protein-coding genes (COIII, ND2, and ND6) of V. fijiensis are under positive selection. Meanwhile, the functional annotation shows that distinctly positive selected orthologs in V. fijiensis are predominately related to neural signal transduction, immunity, antiapoptotic, and energy metabolism. These results indicate that the mitogenomes and key genes found in transcriptomic analysis are under high-temperature and high-pressure conditions, and which may contribute V. fijiensis to have evolved to adapt to the extreme hydrothermal vent environments. The findings shed light on the mitogenome and transcriptome of V. fijiensis, which lays a foundation for the indepth understanding of the adaptation mechanism of sessile invertebrates to the deep-sea environment. [ABSTRACT FROM AUTHOR]