Taxonomy Of Nematodes And Community Structure Of Meiofauna In Various Marine Habitats

Meiofauna is the most abundant among the groups in marine benthic habitats and plays an important role in marine benthic food web. Nematode is the key member of meiofauna, with very high abundance and diversity, but the taxonomy of nematode is one of the most difficult and most insufficient among animal kingdom. The ecological study of meiofauna in China seas is obviously insufficient, studies in the East China Sea and South China Sea are even less, the deep-sea meiofauna in the West Pacific has not been studied. Large numbers of nematodes are still unknown in China seas. DNA Barcoding makes it possible to rapidly classify the marine nematodes, taxonomy of which is labor and time consuming. It is of important scientific significance to explore a suitable fixing method for marine nematodes to combine the data of morphology and molecular perfectly.The study was based on the samples of 72 stations, collecting from Nanji Islands Marine Nature Reserve in four seasons during November 2013 to August 2014, Yangtze Estuary and East China Sea during July and August in 2012, Dongzhai Harbor Mangrove Natural Reserve Area during December 2012, deep-sea area of Okinawa Trough during April 2014 and Yap Seamount; and nematodes in the Taiping Bay, Qingdao. The results of this thesis contains three main parts:1. Taxonomy of free-living nematodesThree new genera were erected: Parachaetonema gen. nov., Paroctonchus gen.nov., Parasynodontoides gen. nov. 10 species belonging six genera were described as new to science, two new combination were proposed.The diagnosis of Parachaetonema gen. nov. is as follows: Anterior sensilla in three circles: six inner labial setae and six outer labial setae, four cephalic setae posteriorly situated at the base of buccal cavity. Buccal cavity toothless, cylindrical and spacious, sclerotized, with only posterior portion surrounded by pharyngeal tissue. Amphid fovea longitudinal groove-shaped with transverse striation. Spicules with gubernaculum apophysis. Many papillate precloacal supplements. Two opposed testes. Only a posterior reflexed ovary. Vulva situated at anterior fourth of body.The diagnosis of Paroctonchus gen. nov. is as follows: Buccal cavity armed with one dorsal and two ventrosublateral teeth with the left ventrosublateral tooth the largest and many small teeth distributed on sclerotized wall of buccal cavity with posterior end surrounded by pharyngeal tissue. Amphidial fovea pocket-like with transverse slit-like aperture in middle portion of buccal cavity. Demanian system absent. Two reflexed ovaries. Two opposed testes. Spicules short and straight, without gubernaculum. Precloacal supplements present. Tail conical-cylindrical.The diagnosis of Parasynodontoides demani gen. nov. is as follows: Head with six conical outer labial papillae and four long and robust cephalic setae. Amphid fovea single loop-shaped, with longitudinal oval outline. Buccal cavity elongate conical without odontia. Two lateral subcephalic setae situated behind base of buccal cavity. Pharynx cylindrical with posterior end swelling. Two opposed testes. Spicules robust and arcuate, cephalated proximally with a hook. Gubernaculum divided into two pieces, the dorsal one with two dorso-caudally directed apophyses and the ventral one tubular. Two outstretched ovaries. Demanian system present, connecting uterus and wall of intestine.The list of new species and new combinations: Epacanthion hirsutum Shi & Xu, 2016 Epacanthion longicaudatum Shi & Xu, 2016 Epacanthion fasciculatum Shi & Xu, 2016Epacanthion sparsisetae Shi & Xu, 2016 Parachaetonema multipapillata sp. nov. Paroctonchus nanjiensis sp. nov. Gammanema magnum sp. nov. Synonchium multidentis sp. nov. Spirobolbolaimus undulatus sp. nov. Parasynodontoides demani sp. nov. Molgolaimus pecticauda(Murphy, 1966) comb. nov. Molgolaimus spirifer(Warwick, 1970) comb. nov.2. Ecology of meiofaunaThe community structure of meiofauna in the studied habitats is mainly influenced by the type of sediment, organic content and water depth. The abundance of meiofauna in the East China Sea is higher than that in the Nanji Islands, but lower than that in Dongzhai Harbor Mangrove; the abundance of meiofauna in the deep-sea area of the Okinawa Trough and Yap Seamount is the lowest. The distribution of biomass of meiofauna is similar to that of the abundance.Nematodes are always the most abundant of meiofauna in these habitats. The proportion of nematodes in Nanji Islands is the lowest, and that in the deep-sea area is the highest.The study of N/C indicates that the sediments of Dasha’ao sand beach and Beigang Mangrove are very clean, sediments of Sanjiang Mangrove and Guoxing’ao mudflat are polluted. The sediment indicated by H’ in Dasha’ao sand beach and Beigang Mangrove was worse than result by N/C.3. Exploration of methods in DNA extraction of marine nematodes based on accurate morphological identificationThe morphology and DNA of marine nematode fixed by the ethanol-glycerin solution are both good enough, and can combine data of molecular biology method and morphological identification reliably to match the need in DNA Barcoding. Thus, the ethanol-glycerin solution is potentially the most suitable method for DNA barcoding study of marine nematode.The main innovation points of this thesis:Meiofauna in various marine benthic habitats, from intertidal sediments to the continental shelf and to the deep sea were studied. Three new genera, ten new species and two new combinations were described. The ecological data of meiofauna in the East China Sea and South China Sea were supplemented and the deep-sea meiofauna in the West Pacific was first studied, providing a foundation for further study on the deep-sea meiofaunal biodiversity and ecology. The methods of fixation and DNA extraction for marine nematodes were preliminary explored, providing the theory support and the foundation for study of DNA barcoding of marine nematode.