Taxonomic And Histologic Studies Of Polydora Complex In The Coastal Area Of China

The taxonomy and histological structure of Polydora complex infesting mollusks in China’s coastal waters such as Dalian, Yantai, Nantong, Wenzhou, Ningbo,Yangjiang, Shenzhen, Zhanjiang, and Lingshui were studied by living observation,histological staining technique, complete mitochondrial genome sequence technique,phylogenetic analyses of multiple molecular and scanning electron microscopy(SEM). The results were as follows:1. the distribution of Polydora complex in coastal watersSeven species of Polydora complex, P.lingshuiensis, P.huplara, P.brevipalpa,P.aura, P.websteri, P.haswelli and Polydora sp, were found in this investigation.P.lingshuiensis was found in Lingshui and Guangdong province. P.hoplura,P.brevipalpa and P.aura were found in Wen Zhou, Da Lian and Yan Tai, respectively.P.websteri was found in Ning Bo and Yang Jiang. P.haswelli was found in Shen Zhen,Zhan Jiang. Polydora sp. was the most widely distributed Polydora complex which was found in both high latitudes waters and low latitudes ones such as Nan Tong,Yang Jiang, Shen Zhen and Zhan Jiang.2.The morphology of Polydora complexThe morphology of P.brevipalpa and P.lingshuiensis was studied by living observation, and scanning electron microscopy(SEM). The resultswere as follows:The common charateristics :(1)the worms translucent and light brown in live,with black pigmentation on the palps. Prostomium round in anterior margin, four eyes in trapezoidal arrangement. Chaetiger 5 modified and enlarged; major spines of chaetiger 5 falcate, with a lateral flange. Branchiae from chaetiger 7, blood vessels flowing in the middle of the body and the branchiae. Pygidium disc-like, with a dorsal incision.(2)SEM showed that the middle of the palps had food groove, within which had a large number of cilia. Occipital tentacle absent. Branchiae Begining from chaetiger 7, dorsal bands of cilia extending across the dorsum, between each pair of branchiae.The neurochaetae were replacey by bidentate hooded hooksfromchaetiger 7.the difference:(1)Median antenna digitiform, located between the bases of palps in P.lingshuiensis,but P. brevipalpa absent.(2)Major spines in the fifth segments of P.lingshuiensis are falcate, without conspicuous flange, with concavity at subterminal ends,but P. brevipalpa with conspicuous flange.3.The histological structure of Polydora complexThe histological structure of P. brevipalpa was studied by histological staining technique. The results were as follows:Histological staining of P.brevipalpa, showed that the body structure was mainly composed of skin, muscle layer, and the digestive system. The stratum corneum of skin was obviously thick in head,and the muscle in head was stronger than other parts.A lot of gland cells were concentrated in cuticular layers. The muscle system was highly developed, and oblique muscle present. The villi on Epithelial cells of the digestive tube present densely and regularly named striated border were obvious, and each segment had a pair of renal tubular, lateral vessel, and glandular pouch,respecitvely.Renal tube appeared in the excretory system, with the renal mouth opening in the body cavity, the other side opening on the body surface. Despite the dorsal vessel,there are a lot of lateral blood vessels and capillaries in it,and with completely closed vascular system;In digestive system, the pharynx expanded into three cavity, two tentacles cavity and a primary cavity. Intestinal structure was divided into four layers,are: outer membrane layer, muscular layer, submucosa, and mucous membrane.In combination with the anatomy and histology, the study showed that the boring mechansm of P.brevipalpa is combined result of both mechanical abrasion and chemical action.4. Complete mitochondrial genome sequence of Polydora complexComplete mitochondrial genome sequence of Polydora complex accomplished by long PCR. There were 17609 bp in the complete mitochondrial genome sequence.The software DOGMA was used to predict ribosomal RNA and protein coding genes of Polydora complex, and the software t RNAscan-SE 1.21 was used to predict transfer RNA genes of Polydora complex. The results were as follows:There are 38 genes in NT-n.sp’s mitochondrial genome, including 13protein-coding genes, 23 transit RNA genes and two ribosomal RNA genes.Polydora sp. had methionine transfer RNA genes than annelid.Contained 21non-coding regions, with four large non-coding regions,and the remaining distributein the other areas of the mitochondria.