VARIABILITY OF THE GROUND MOLLUSK SHELL

The variability of conchiological characters of the shell of the terrestrial mollusk Chondrula tridens (Müller 1774) from 4 different types of landscapes of the Ulyanovsk region was studied. Analysis of elementary characters, proportions and wellhead armament of shell structures demonstrates a significant heterogeneity of the species. The large size of the shell of the snails is explained by an increase in the growth period due to an increase in temperature and humidity in the conditions of the north-western and southern landscapes of the Ulyanovsk region, as well as in the urbanized environment. Reducing the height of the shell, increasing roundness and better development of the mouth teeth of mollusks living in the chalk steppe reflects their adaptability to the conditions of more xerothermic landscapes, and also determines the position of the shell in space.

Geographical and chronological variability of the conchological characters of the mollusc Fruticicola fruticum (O.F.Müller, 1774) (Gastropoda; Pulmonata; Bradybaenidae) in the Eastern Europe

The population structure of the terrestrial mollusk (Gastropoda, Pulmonata, Bradybaenidae) in different landscapes of Eastern Europe on the basis of conchological measurements, including morphometric parameters and color variants was studied. For all morphometric parameters used, statistically significant differences were found between the studied populations. At the same time, the shell size are determined not by zonal characteristics, but by microbiotopic conditions. Changes in the frequency of shell phenotypes in Fr. fruticum populations are probably of a multifactorial nature. The ratio of different color variants can be caused by the influence of radiation, cyclic fluctuations of climatic factors, succession changes in biotopes, and gene drift.

A chromosomal-level genome assembly for the giant African snail Achatina fulica

BackgroundAchatina fulica, the giant African snail, is the largest terrestrial mollusk species. Owing to its voracious appetite, wide environmental adaptability, high growth rate, and reproductive capacity, it has become an invasive species across the world, mainly in Southeast Asia, Japan, the western Pacific islands, and China. This pest can damage agricultural crops and is an intermediate host of many parasites that can threaten human health. However, genomic information of A. fulica remains limited, hindering genetic and genomic studies for invasion control and management of the species.FindingsUsing a k-mer–based method, we estimated the A. fulica genome size to be 2.12 Gb, with a high repeat content up to 71%. Roughly 101.6 Gb genomic long-read data of A. fulica were generated from the Pacific Biosciences sequencing platform and assembled to produce a first A. fulica genome of 1.85 Gb with a contig N50 length of 726 kb. Using contact information from the Hi-C sequencing data, we successfully anchored 99.32% contig sequences into 31 chromosomes, leading to the final contig and scaffold N50 length of 721 kb and 59.6 Mb, respectively. The continuity, completeness, and accuracy were evaluated by genome comparison with other mollusk genomes, BUSCO assessment, and genomic read mapping. A total of 23,726 protein-coding genes were predicted from the assembled genome, among which 96.34% of the genes were functionally annotated. The phylogenetic analysis using whole-genome protein-coding genes revealed that A. fulica separated from a common ancestor with Biomphalaria glabrata ∼182 million years ago.ConclusionTo our knowledge, the A. fulica genome is the first terrestrial mollusk genome published to date. The chromosome sequence of A. fulica will provide the research community with a valuable resource for population genetics and environmental adaptation studies for the species, as well as investigations of the chromosome-level of evolution within mollusks.