Studies On The Biology And Genetic Analysis Of Craspedacusta Sowerbyi Of Zhejiang

Craspedacusta are a kind of primitive and lower invertebrate that are significant in science and enjoyment. The identification and classification of species of Craspedacusta were mostly based on the observation of morphological characters, which varied with different phases of growth and development and difference of living environments. There have had much argument about the classification of species of Craspedacusta. This paper discussed the morphological characters and classification status of Craspedacusta sp. of Yuhu, Hangzhou and Yangshan, Shaoxing(were identified as C. sowerbyi) based on morphology and molecular biology, which provided molecular-level evidence for the classification of C. sp.. And it systematically investigated the gonad development and ultrastructures of epithelial tissues and cnidoblast of C. sowerbyi of Hangzhou.The main results are as follows:1. The morphologically identification characters of Craspedacusta sp. of Hangzhou and Shaoxing include that, the tentacles are divided into three orders and perradial tentacles are longer than others, nematocyst warts are papilla-shaped and have a spiral arrangement on the tentacle, statocysts are tubular and gonads are long pocket-like. These characters are basically consistent with those of C. sowerbyi. So C. sp. of Hangzhou and Shaoxing are identified as C. sowerbyi Lankester,1880.2. The quantitatively morphological characters of C. sowerbyi of Hangzhou were recorded and analyzed. According to the statistic results, the regression equation between the diameter of umbrella and the width of velum is y=0.0703x+0.555(R~2=0.3737,P = 0.000<0.001), the regression equation between the diameter of umbrella and the number of statocyst is y=5.9479x+53.641 (R~2=0.2461,P = 0.014<0.05), and the regression equation between the diameter of umbrella and the number of tentacle is y=11.743x+181.93(R~2=0.2776,P = 0.008<0.01). There are all significantlyor most significantly linear positive correlations between them while the correlation between the number of statocyst and the number of tentacle is not significant. The sex of C. sowerbyi has no significant effects on the diameter of umbrella and the width of velum.3. According to the results of sequence alignment, the small subunit ribosomal RNA gene sequences of C. sp. of Hangzhou and Shaoxing are most similar to that of C. sowerbyi and the similarity percent are 99.61% and 99.45% respectively. The pairwise genetic distance between C. sp. of Hangzhou or Shaoxing and C.sowerbyi are both, 0.001. The molecular phylogenetic tree shows 100% degree of confidence of branch between C.sp. of Hangzhou and Shaoxing, and C.sowerbyi. Summarily, C.sp. of Hangzhou and Shaoxing are C.sowerbyi. The conclusions are consistent with the result of morphological taxonomy.4. The development of male gonad includes primary spermatocyte, second spermatocyte, spermatid and sperm. The sperm is typically flagellate and consists of head, neck and tail. The head part possesses a narrow and triangular nucleus of high electron-density and has many vertically-arranged granules in the bilateral side of nucleus, but no acrosome. The neck part is composed of four or five big mitochondria and centriole that is surrounded by mitochondria. There are nine satellites from the dense matrix between the triplet microtubules of centriole and three strands of satellite on the end of each satellite. The tail part, namely the flagellum, is long. The axoneme has 9><2+2 arrangement of microtubules. The lateral fins appear on the flagellum.5. The primary oocytes are in the vitellogenesis and have many yolk granules of different electron-density. In the vitellogenesis, mitochondria, rough endoplasmic reticulum and ribosomes are concerned with the formation of yolk granules all the time. Golgi complexes appear in the latter phase and participate in the formation of yolk. Follicle cells transfer yolk materials to oocytes through two pathways. One is that follicle cell is contiguous withoocyte through finger-like cellular channels to transfer yolk granules to oocyte, the other is that follicle cells expel yolk granules to follicle lumen through exocytosis and then these granules are transferred into the oocytes through endocytosis.6. The structure of tentacle and somatic layer of C. sowerbyi follow the mode of two-blastoderm of Cnidaria that consists of ectoblast, endoblast and mesoglea. The external epitheliomuscular cell layer has high electron-density while internal epitheliomuscular cell layer has low electron-density and typically inverse T shape. The cell junctions between epitheliomuscular cells are septate junctions and desmosome. Developed microvilli appear on the free surface of internal epitheliomuscular cells of somatic layer while few on the free surface of internal epitheliomuscular cells of tentacle. There are developed myofibrils in the bases of internal and external epitheliomuscular cells that have an orthogonal distribution. Both mesoglea consist of many thin fibrils and tiny granules from the secretion of internal and external epitheliomuscular cells.7. There are two kinds of cnidoblasts in C. sowerbyi, namely glutinant nematocyst and penetrant nematocyst. In the development of nematocyst, there is low electron-density material in the nematocyst at first and the electron-density increases gradually. Finally, many a small masses of material appear and form the crimped nematocyst threads gradually. The centriole is observed in the penetrant nematocyst. Big mitochondria with developed cristaes are observed in the back of cnidoblast for the first time. These mitochondria provide energies for the release of nematocyst threads.