Bivalves are species-rich mollusks with prominent protective roles in coastal ecosystems. Across these ancient lineages, colony-founding larvae anchor themselves either by byssus production or by cemented attachment. The latter mode of sessile life is strongly molded by left-right shell asymmetry during larval development of Ostreoida oysters such as Crassostrea hongkongensis. Here, we sequenced the genome of C. hongkongensis in high resolution and compared it to reference bivalve genomes to unveil genomic determinants driving cemented attachment and shell asymmetry. Importantly, loss of the homeobox gene Antennapedia (Antp) and broad expansion of lineage-specific extracellular gene families are implicated in a shift from byssal to cemented attachment in bivalves. Comparative transcriptomic analysis shows a conspicuous divergence between left-right asymmetrical C. hongkongensis and symmetrical Pinctada fucata in their expression profiles. Especially, a couple of orthologous transcription factor genes and lineage-specific shell-related gene families including that encoding tyrosinases are elevated, and may cooperatively govern asymmetrical shell formation in Ostreoida oysters.

The giant triton snail (Charonia tritonis), an endangered gastropod species of ecological and economic importance, is widely distributed in coral reef ecosystems of the Indo-West Pacific region and the tropical waters of the South China Sea. Limited research on molecular mechanisms can be conducted because the complete genomic information on this species is unavailable. Hence, we performed transcriptome sequencing of theC. tritonisfoot muscle and mantle using the Illumina HiSeq sequencing platform. In 109,722 unigenes, we detected 7,994 (3,196 up-regulated and 4,798 down-regulated) differentially expressed genes (DEGs) from theC. tritonisfoot muscle and mantle transcriptomes. These DEGs will provide valuable resources to improve the understanding of molecular mechanisms involved in biomineralization ofC. tritonis.In the Gene Ontology (GO) database, DEGs were clustered into three main categories (biological processes, molecular functions, and cellular components) and were involved in 50 functional subcategories. The top 20 GO terms in the molecular function category included sulfotransferase activity, transferring sulfur-containing groups, and calcium ion binding, which are terms considered to be related to biomineralization. In KEGG classifications, transcriptomic DEGs were mainly enriched in glycosaminoglycan biosynthesis-chondroitin sulfate/dermatan sulfate, and sulfur metabolism pathway, which may be related to biomineralization. The results of qPCR showed that three of the eight genes examined were significantly up-regulated in the mantle. The phylogenetic tree of BMP1 suggested a significant divergence between homologous genes inC. tritonis. Our results improve the understanding of biomineralization inC. tritonisand provide fundamental transcriptome information to study other molecular mechanisms such as reproduction.

Peptidoglycan recognition proteins (PGRPs) are a family of pattern recognition receptors (PRRs) involved in host antibacterial responses, and their functions have been characterized in most invertebrate and vertebrate animals. However, little information is available regarding the potential function of PGRPs in the giant triton snail Charonia tritonis. In this study, a short-type PGRP gene (termed Ct-PGRP-S1) was identified in C. tritonis. Ct-PGRP-S1 was predicted to contain several structural features known in PGRPs, including a typical PGRP domain (Amidase_2) and Src homology-3 (SH3) domain. The Ct-PGRP-S1 gene was constitutively expressed in all tissues examined except in proboscis, with the highest expression level observed in the liver. As a typical PRR, Ct-PGRP-S1 has an ability to degrade peptidoglycan (PGN) and was proven to have non-Zn²⁺-dependent amidase activity and antibacterial activity against Vibrioalginolyticus and Staphylococcus aureus. It is the first report to reveal the peptidoglycan recognition protein in C. tritonis, and these results suggest that peptidoglycan recognition protein Ct-PGRP-S1 is an important effector of C. tritonis that modulates bacterial infection resistance of V. alginolyticus and S. aureus, and this study may provide crucial basic data for the understanding of an innate immunity system of C. tritonis.

The giant triton snail (Charonia tritonis) is widely distributed in tropical coral reefs in the Indo-West Pacific. Its distribution areas in China include the Penghu Islands, Hengchun Peninsula, and Xisha Islands. In this study, we use Multivariate Analysis of Variance (MANOVA) to compare the live weight and shell length between different shell colors of C. tritonis. In addition, we conducted sequence analysis of the mitochondrial cytochrome oxidase (COI) gene to assess the affinity of C. tritonis with two different shell colors based on the sample we obtained. Then, we constructed phylogenetic trees using the maximum likelihood (ML) and Bayesian Inference methods, and constructed haplotype network diagrams. In addition, we performed Tajima’s D and Fu’s neutrality tests. The results show that The Partial mitochondrial COI sequences of 28 C. tritonis were all 603 base pairs in length, and seven haplotypes were detected from the samples, besides, the gene flow was calculated to be 11.78, the genetic differentiation coefficient was 0.02078. Our results indicated that the population size of C. tritonis remained relatively stable. Besides, the genetic and size differentiation between the two different shell colors was small, and individuals of C. tritonis with different shell colors belong to the same genetic clade. In fact, the two morphotypes could not be distinguished by both genetic and morphometric data. The mitochondrial COI gene fragments of the two different shell colors were sequenced and analyzed to accumulate information about the population genetics of C. tritonis and to provide a scientific basis for the conservation of its species resources.The giant triton snail (Charonia tritonis) is widely distributed in tropical coral reefs in the Indo-West Pacific. Its distribution areas in China include the Penghu Islands, Hengchun Peninsula, and Xisha Islands. In this study, we use Multivariate Analysis of Variance (MANOVA) to compare the live weight and shell length between different shell colors of C. tritonis. In addition, we conducted sequence analysis of the mitochondrial cytochrome oxidase (COI) gene to assess the affinity of C. tritonis with two different shell colors based on the sample we obtained. Then, we constructed phylogenetic trees using the maximum likelihood (ML) and Bayesian Inference methods, and constructed haplotype network diagrams. In addition, we performed Tajima’s D and Fu’s neutrality tests. The results show that The Partial mitochondrial COI sequences of 28 C. tritonis were all 603 base pairs in length, and seven haplotypes were detected from the samples, besides, the gene flow was calculated to be 11.78, the genetic differentiation coefficient was 0.02078. Our results indicated that the population size of C. tritonis remained relatively stable. Besides, the genetic and size differentiation between the two different shell colors was small, and individuals of C. tritonis with different shell colors belong to the same genetic clade. In fact, the two morphotypes could not be distinguished by both genetic and morphometric data. The mitochondrial COI gene fragments of the two different shell colors were sequenced and analyzed to accumulate information about the population genetics of C. tritonis and to provide a scientific basis for the conservation of its species resources.

It has been reported that the giant triton snail (Charonia tritonis) inserts its large proboscis and then injects venom or acid saliva from its salivary gland into its prey, the crown-of-thorns starfish Acanthaster planci (COTS), paralyzing it. A full-length cDNA sequence of the C. tritonis Ct-kunitzin gene was obtained by RACE PCR based on a transcriptomic database constructed by our laboratory (data not published), which contains an open reading frame (ORF) sequence with a length of 384 bp including a 1–32aa Kunitz domain. The Ct-kunitzin peptide was synthesized by solid-phase polypeptide methods according to its conserved amino acid sequence, with a molecular weight of 3746.0 as well as two disulfide bonds. Renatured Ct-kunitzin was injected into mice ventricles to evaluate its potential function. Compared with the normal control group (physiological saline), the spontaneous locomotor activity of the Ct-kunitzin group decreased significantly. There was a significant effect on Ct-kunitzin on mice grip strength in the grip strength test. In addition, Ct-kunitzin exhibited remarkable biological activity in suppressing pain in the pain thresholds test. There were no significant differences between the Ct-kunitzin group and the normal control group in terms of various hematological indexes and histopathological observations. When tested in COTS, the most significant histological change was the destruction, disorganization, and significant reduction in the amount of COTS tube feet tissues. Altogether, the potential paralyzing effect on mice suggests that Ct-kunitzin is a possible agent for novel drug development.