Genome of the tardigrade Cucumibius annulatus: functional annotation and specific proteins

Tardigrades are microscopic invertebrates renowned for their capacity to survive extreme environmental conditions, yet stress tolerance strategies vary substantially across the phylum. Here we present the first genome assembly and annotation for the superfamily Isohypsibioidea - the most basal group within the order Parachela - represented by freshwater species Cucumibius annulatus. The draft genome (73 Mb, N50 = 96.4 kb, BUSCO 87.1%) was assembled from short-read data. Orthogroup-based comparison against three reference tardigrades and two ecdysozoan outgroups (Caenorhabditis elegans, Drosophila melanogaster) identified a set of orthogroups unique to C. annulatus. Canonical tardigrade heat-soluble protein families (CAHS, SAHS, MAHS) are present but at lower copy numbers than in other sequenced Parachela, and trehalose biosynthesis enzymes are absent, consistent with the non-anhydrobiotic lifestyle of the species. This study provides a genomic resource for a newly established genus and a comparative framework for interpreting ancestral genomic features of Parachela.