Crustacean amphipods are important trophic links between primary producers and higher consumers. although most amphipods occur in or around aquatic environments, the family talitridae is the only family found in terrestrial and semi-terrestrial habitats. the sand-hopper Trinorchestia longiramus is a talitrid species often found in the sandy beaches of South Korea. In this study, we present the first draft genome assembly and annotation of this species. We generated ~380.3 Gb of sequencing data assembled in a 0.89 Gb draft genome. Annotation analysis estimated 26,080 protein-coding genes, with 89.9% genome completeness. Comparison with other amphipods showed that T. longiramus has 327 unique orthologous gene clusters, many of which are expanded gene families responsible for cellular transport of toxic substances, homeostatic processes, and ionic and osmotic stress tolerance. This first talitrid genome will be useful for further understanding the mechanisms of adaptation in terrestrial environments, the effects of heavy metal toxicity, as well as for studies of comparative genomic variation across amphipods. Background & SummaryAmphipoda is an order of malacostracan crustaceans, composed of more than 228 families with over 10,200 species 1 . Most members of Amphipoda are found in aquatic environments, with both freshwater and marine species that occur in diverse habitats 2-6 . However, only a few amphipods in the family Talitridae are found in terrestrial regions close to the water, and others are "semi-terrestrial, " with both littoral and terrestrial representatives 7 .Talitrids are one of the prevailing macrofaunal groups in coastal regions that live along the interface between the water and land. The coastal talitrids, also known as "sand-hoppers, " are considered key species for energy flow to higher trophic levels 8 . They play a crucial role in food web dynamics by feeding on algal-biomass 9 and detritus along sandy beaches. They then become the source of food for many invertebrates, fish, and birds 4,8 . Unfortunately, anthropogenic activity contributes to various types of pollutants in the coastal ecosystem, which impacts the survival of talitrids 10-12 and other macrofauna [13][14][15] . For this reason, many talitrids are used as model organisms for studies of metal toxicity 10-12 . In addition, previous work on talitrids examined levels of genetic variation 16,17 , behavioral adaptations 18 , osmoregulation 19 , and orientation studies 20 . Most of these studies were carried out along the North Sea and the Mediterranean Sea regions.Despite such biological and ecological significance, no genome studies have been performed on any talitrid species, and only three genomes have been studied among the entire amphipod order. These included (1) Eulimnogammarus verrucosus (Family: Eulimnogammaridae) 21 , a freshwater amphipod from Baikal Lake; (2) Hyalella azteca (Family: Hyalellidae) 22 , another freshwater amphipod that lives by burrowing in the sediments; and (3) Parhyale hawaiensis (Family: Hyalidae) 23 . Tr...

Background The shuttles hoppfish (mudskipper), Periophthalmus modestus, is one of the mudskippers, which are the largest group of amphibious teleost fishes, which are uniquely adapted to live on mudflats. Because mudskippers can survive on land for extended periods by breathing through their skin and through the lining of the mouth and throat, they were evaluated as a model for the evolutionary sea-land transition of Devonian protoamphibians, ancestors of all present tetrapods. Results A total of 39.6, 80.2, 52.9, and 33.3 Gb of Illumina, Pacific Biosciences, 10X linked, and Hi-C data, respectively, was assembled into 1,419 scaffolds with an N50 length of 33 Mb and BUSCO score of 96.6%. The assembly covered 117% of the estimated genome size (729 Mb) and included 23 pseudo-chromosomes anchored by a Hi-C contact map, which corresponded to the top 23 longest scaffolds above 20 Mb and close to the estimated one. Of the genome, 43.8% were various repetitive elements such as DNAs, tandem repeats, long interspersed nuclear elements, and simple repeats. Ab initio and homology-based gene prediction identified 30,505 genes, of which 94% had homology to the 14 Actinopterygii transcriptomes and 89% and 85% to Pfam familes and InterPro domains, respectively. Comparative genomics with 15 Actinopterygii species identified 59,448 gene families of which 12% were only in P. modestus. Conclusions We present the high quality of the first genome assembly and gene annotation of the shuttles hoppfish. It will provide a valuable resource for further studies on sea-land transition, bimodal respiration, nitrogen excretion, osmoregulation, thermoregulation, vision, and mechanoreception.

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