Study On Morphological Characteristics And Adaptive Evolution Of Gladius, Stylets And Cuttlebones Of Cephalopods

As the third biggest class of Mollusca, Cephalopod appears 500 million years from Cambrian.There are more than 700 existent species divided into Nautiloidea and Coleoidea. Endoskeleton is an important hard tissue of Cephalopod. It can be separated into squid, stylets and cuttlebone according to their different textures. The different morphological characteristics of endoskeleton might be applied into the taxlogy. And it is an important tissure in studying age and growth. Aming at offering basic information for resource protection, and providing refereces for adaptive evolution, studies in this thesis were gladius, stylets and cuttlebone.To clarify the characterization of cuttlebone of Sepia esculenta in the early development, some data were collected at different stages, including red-bead and black- beads stage, heart beating stage, hatching stage, newly emerged larvae stage, 5-day old stage and 10-day old stage. Principalcomponent analysis was performed for the evaluation of seven growth traits of dorsol mantle length, mantle breadth, body weight, cuttlebone length, cuttlebone breadth, cuttlebone weight, lamella number. The results showed that all factors kept significant correlations between any two traits at red-bead and black- beads stage, hatching stage and 10-day old stage.However, some growth traits showed no significant at heart beating stage, newly emerged larvae stage and 5-day old stage. The first principal component reflects the weight factor at the first two stage, while that reflects the length factor at other four stages, respectively. The second principal component reflects the length factor and width factor. The third principal component reflects the width factor mostly. Only two stage have the fourth principal component, which the factors are lamella factor and width factor. The growth rate of growth traits of Sepia esculenta was not the same at different stage. From red-bead and black-bead stage to heart beating stage, the growth of morphometric traits was prior to body weight, while the growth of body weight overtook the morphometric traits from hatching stage to 10-day old stage.Research on the endoskeleton microstructure was conducted in six species of cephalopods using the scanning electron microscopy(SEM). Result showed those endoskeleton can be divided into cuttlebone and squid according to their different textures.The endoskeleton of Spica esculenta, Sepiella maindroni and Spica andreana were cuttlebone. All of them were composed by crystal, but the sharp and the arrangement of crystals varied in different species. The endoskeleton of Loliolus beka, Uroteuthis edulis and Rossia pacific were squid which were composed by non-crystal material, and the the microstructure of these three species are very similar. Cyttlebone owned a larger volume had "gas chamber" Structure compared with squid.The mitochondrial cytochrome coxidase subunit 1(COI) gene sequences of Cephalopoda were selected out from Genbank. A total of 242 sequences from 101 species of 44 genera in Cephalopoda were used as barcoding and verifyed for the availability of using DNA barcoding to identify species. Base composition, base substitutions, and genetic distance were calculate by C lustal X and MEGA6.0. The results indicated that the mean T, C, A, and G contents were 36.4%, 19.6%, 28.8%, and 15.2%, respectively, base composition was biased. DN A barcoding can be used to identify species if the distance between interspecific is much larger than that between intraspecific and different individuals of the same species are clustered in monophyletic group. The interspecific and intraspecific genetic distances were 0.121 and 0.004, respectively, and the interspecific distance was 30.25 times that of the intraspecific distance. In some taxa, DNA barcoding could not discrimin ate intra- and interspecific variation when intraspecific genetic distances were not large enough. In this study, the phylogenetic analysis showed that 98.0% of the Cephalopoda were monophyletic. It suggested that the NJ tree based on COI has a high discrimination in classification species. In a high level of taxa, the difference between COI molecular marker results and traditional classification results are increased. There are some differences in the classification of family compared the COI molecular marker and endoskeleton marker.