Analysis of Diversity of CO I Gene and System Generation of Nine Species of Chitons

Cytochrome c oxidase subunit 1 （CO I ） genes from 9 chiton species in China＇s coast area were sequenced. A phylogeny tree about these gene sequences were reconstructed together with other 4 CO I gene sequences of chitons from Genbank. The affin- ity genetic relationship and the taxonomic status of molecular evolution for these 13 chiton species were analyzed. The results show that Liolophura japonica and Onithochiton hirasei belong to Chitonidae, .4canthochiton rubrolineatus and Acanthochiton dis- similis belong to Acanthochitonidae, and Placiphorella japonica and Mopalia retifera belong to the same family Mopliidae. How- ever, Lepidozona coreanica, Ischnochiton comptus, and lschno- chiton hakodadensis are not supposed to be referred to Ischnochi- tonidae according to the genetic distance analysis （L. coreanica, 1. comptus, and 1. hakodadensis are usually classed as Ischnochi- tonidae according to their morphological character）. Furthermore, 1. hakodadensis could not been classed as lschnochiton, and it is more likely to be treated as a close relative of Lepidozona.

Report of a chiton in the genus Leptochiton (Lepidopleurida:Lepidopleurina:Leptochitonidae) from the Yap Trench in the West Pacific Ocean

Two chiton specimens were collected from sedimentary habitat by China＇s manned Jiaolong submersible diving to a depth of 6 754 m in the north of the Yap Trench. This is a new locality record for chiton. Both morphological and molecular data support that the two specimens are the same species belonging to the genus Leptochiton. Morphologically, this species strongly resembles L. vanbellei and L. deforgesi. Phylogenetically, it has a close evolutionary relationship with L. vanbellei, L. deforgesi and L. boucheti. This is the third deepest record for deepsea chitons so far.

Characterization of Chiton Ischnochiton hakodadensis Foot Based on Transcriptome Sequencing

Chiton(Ischnochiton hakodadensis) is one of marine mollusks well known for its eight separate shell plates. I. hakodadensis is important, which plays a vital role in the ecosystems it inhabits. So far, the genetic studies on the chiton are scarce due in part to insufficient genomic resources available for this species. In this study, we investigated the transcriptome of the chiton foot using Illumina sequencing technology. The reads were assembled and clustered into 256461 unigenes, of which 42247 were divided into diverse functional categories by Gene Ontology(GO) annotation terms, and 17256 mapped onto 365 pathways by KEGG pathway mapping. Meanwhile, a set of differentially expressed genes(DEGs) between distal and proximal muscles were identified as the foot adhesive locomotion associated, thus were useful for our future studies. Moreover, up to 679384 high-quality single nucleotide polymorphisms(SNPs) and 19814 simple sequence repeats(SSRs) were identified in this study, which are valuable for subsequent studies on genetic diversity and variation. The transcriptomic resource obtained in this study should aid to future genetic and genomic studies of chiton.

Phylogenomic analyses shed light on the relationships of chiton superfamilies and shell‑eye evolution

Mollusca is the second-largest animal phylum with over 100,000 extant species representing eight classes.Across 1000 extant species in the class Polyplacophora,chitons have a relatively constrained morphology but with some notable deviations.Several genera possess“shell eyes”,i.e.,true eyes with a lens and retina that are embedded within the dorsal shells.The phylogeny of the major chiton clades is mostly well established,in a set of superfamily-level and higher level taxa supported by various approaches,including morphological studies,multiple gene markers,mitogenome-phylogeny,and phylotranscriptomic approaches.However,one critical lineage has remained unclear,namely Schizochiton which was controversially suggested as being the potential independent origin of chiton shell eyes.Here,with the draft genome sequencing of Schizochiton incisus(superfamily Schizochitonoidea)plus assemblies of transcriptome data from other polyplacophorans,we present phylogenetic reconstructions using both mitochondrial genomes and phylogenomic approaches with multiple methods.We found that phylogenetic trees from mitogenomic data are inconsistent,reflecting larger scale confounding factors in molluscan mitogenomes.However,a consistent and robust topology was generated with protein-coding genes using different models and methods.Our results support Schizochitonoidea as the sister group to other Chitonoidea in Chitonina,in agreement with the established classification.Combined with evidence from fossils,our phylogenetic results suggest that the earliest origin of shell eyes is in Schizochitonoidea,and that these structures were also gained secondarily in other genera in Chitonoidea.Our results have generated a holistic review of the internal relationship within Polyplacophora,and a better understanding of the evolution of Polyplacophora.