Systematics On Some Groups Of Terrestrial Mollusks

Terrestrial gastropods are a group of land dwelling animals in the phylum Mollusca.They play an important role in the food chain of terrestrial ecosystem as part of the soil fauna.Due to their often specific ecological requirements and limited dispersal abilities,many land snails are susceptible to habitat change.Hence,they are considered as suitable bioindicators for the monitoring of environment change.Due to their low migration rates,land snails are considered interesting model organisms in biogeographical studies.Terrestrial mollusks represent a significant proportion of zoological diversity and have evolved from non-terrestrial ancestors multiple times independently.Traditionally,the classification of terrestrial mollusks was mainly based on shell morphological characteristics.However,the shell-based taxonomy,including species identification,is fraught with difficulties because shell characteristics may be influenced by environmental attributes.In addition,phylogenetic relationships among the taxonomic ranks,which are higher than genus level,have remained controversial,leading to systematic confusion.The complete mitogenomes of representative species of each the Cyclophoridae and Philomycidae were sequenced,and their phylogenetic relationships within Stylommatophora and Architaenioglossa,respectively,were reconstructed.Furthermore,I reviewed the taxonomic classification of tree snails of the genus Amphidromus from East Timor and described seven new species based on material from the collections of the Australian Museum.In addition,the phylogenetic relationships of the genus Pupoides were reconstructed based on COI and 16 S data,and I explored the evolutionary significance of changes in shell chirality(i.e.,the left–right reversal of shell coiling)in this group.Main results of my studies are as follows:1.The complete mitochondrial genome of the Chinese slug Meghimatium bilineatum is 13,972 bp long.The base composition of the heavy strand is A = 31.89 %,T = 39.55 %,C = 13.92 %,and G = 14.64 %.The AT-content(71.44 %)is distinctly higher than the GC-content(28.56 %).A novel and unique mitochondrial gene order in Meghimatium bilineatum was found,which differs significantly from gene orders thus far reported for other stylommatophorans.Phylogenetic reconstructions based on the sequences of all protein-coding genes consistently recovered Stylommatophora as a well-supported clade and within Stylommatophora supporting a sister-group relationship of the two suborders Achatinina and Helicina.Arionoidea has been found in a sister-group relationship with the Succineidae(Succineoidei).2.The complete mitochondrial genome of the Chinese land snail Cyclophorus martensianus is 15,308 bp long.The base composition of the whole heavy strand is A = 29.12%,T = 40.48%,C = 14.07%,and G = 16.33%.The AT content(69.60%)is distinctly higher than the GC content(30.40%).Our data confirmed the paraphyly of the so-called ‘Architaenioglossa',a diverse and ancient group of non-marine caenogastropods.Our study also confirmed a conserved mitochondrial gene order within Architaenioglossa.3.Combining analyses of geometric morphometry,reproductive anatomy and molecular data on Amphidromus tree snails distributed in East Timor,I revised the taxonomy of this group and described seven new species,including A.lautemensis sp.nov.,A.baucauensis sp.nov.,A.kessneri sp.nov.,A.bobovalima sp.nov.,A.viquequensis sp.nov.,A.brandontrani sp.nov.,and A.tetum sp.nov.4.Bayesian Inference and Maximum Likelihood analyses of mitochondrial sequences revealed the paraphyly of Pupoides.Pupoides albilaris,the type species of Pupoides from North America,was found to group together with Vertigo(Vertiginidae).By contrast,the Australian species of Pupoides were found to be the sister group of Pupilla(Pupillidae).Based on this finding,we concluded that the North American Pupoides and Australian Pupoides have different origins and are not members of the same evolutionary group.Phylogenetic analyses indicated that sinistral(i.e.,left–handed coiling of shells)have evolved at least three times in a group of otherwise dextral(right-handed)species.The dextral species P.adelaidae,which is distributed in central Australia,has sinistral populations.We propose that changes in the coiling direction of the shell may be a multi-origin random event rather than a morphological synapomorphy in the evolutionary history of sinistral species.Therefore,chirality of the shell may not be a reliable character for the taxonomic classification in this group.