Morphology, Nolecular Characterization And Geographical Distribution Of Polydora Websteri

Spionid worms of the genus Polydora inhabited the shells of many commercially important bivalves which severely affected normal growth and development of the hosts in molluscan aquaculture. Polydorins are members of the Polydora complex, a speciose group comprising more than 140 described species within nine genera belonging to the Spionidae.A study was made of the Morphology,molecular characterization and geographical distribution of Polydora Websteri infesting mollusks.This study is the first to molecularly validate unidentified larvae from the aquatic environment through the known COI sequences of adults. The main results are summarized as follows.1. The morphology of Polyora websteri were studied by living observation and scanning electron microscopy(SEM). The purpose of the study was to accumulate more material for the taxonomy of polydora complex(polychaetea). The results showed that the Polydora websteri bores U-shaped burrows which never branch; The living observation and SEM showed that the live worm was translucent and light brown, with black pigmentation on the palps, Prostomium weakly incised anterior ly, caruncle extending to end of setiger 2 or middle of setiger 3 in sampling specimens, eyes present or absent, if present, up to four, trapezoidal in arrangement, Setiger 1 without notosetae, Chaetiger 5 modified and enlarged, major spines of chaetiger 5 falcate, Branchiae and hooded hooks from setiger 7, Pygidium flaring disc with dorsal notch.2. Polydora lingshuiensis and P. websteri were compared to each other for precise identification using the techniques of morphology and molecular biology. Their geographical distributions were also investigated. Morphologically,P. lingshuiensis can be differentiated from P. websteri in that P. lingshuiensis has one median antenna on the caruncle and one concavity at subterminal end of major spine, whereas P. websteri has no median antenna, and had lateral flange on major spine. Distance analyses indicate that the interspecific distance of P. lingshuiensis and P. websteri are evident greater than their intraspecific distance based on nucleus 18 S gene, mitochondrial COⅠ and Cyt b gene. Distance ratio between interspecific and intraspecific polydorins is much greater based on mitochondrial COⅠ and Cyt b gene than nucleus 18 S gene. Mitochondrial COⅠ and Cyt b gene have wider. barcoding gap and higher resolution than nucleus 18 S gene, so they are more suitable for assistant identification of morphologically similar polydorins.3. The oyster-boring pest Polydora websteri is described in detail in the present study for future unambiguous identification using an integrative taxonomic approach that combines morphology and the mitochondrial cytochrome c oxidase subunit 1(COI) gene. Adult P. websteri exhibit a high degree of morphological plasticity in the palp pigmentation, anterior edge of the prostomium, major spines on chaetiger 5, and the shape of the pygidium. The COI gene sequence demonstrated that the intraspecific distance of adults and larvae was-6.64%, whereas the the interspecific distance of adults and larvae was 106.65%. Our results demonstrate that not only did all COI sequences from the larvae show greater than 99% sequence identity to those from adults, but some larvae share the same haplotypes as adults. These findings clearly indicate that the larvae collected from sea waters around an oyster farm belong to P. websteri, the same species as the adult worms collected from the oyster Crassostrea hongkongensis in that locality. Two polydorin-specific primers were successfully designed, or the first time, to amplify target fragments of the COI gene. This study is the first to molecularly validate unidentified larvae from the aquatic environment through the known COI sequences of adults.4. The biology of Polyora websteri were studied by feeding biology, tolerance of the different salinity. Polydora lingshuiensis and P. websteri were compared to each other for investigate their geographical distributions. The results showed that There was difference of feeding biology about fairy shrimp and Chlorella vulgaris; The salinity range of 24 h survival was 15PPt~45PPt; P. lingshuiensis and P. websteri are low host- specificity and widespread along China’s coastal waters. Their transmissions are closely related to culture manner and commercial transportation of their hosts.