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

Tardigrades, or water bears, are microscopic invertebrates renowned for their ability to survive extreme environmental conditions through a process called cryptobiosis. The genomic underpinnings of this remarkable resilience are a subject of intense scientific interest. In this study, we present the first genome assembly and annotation of a tardigrade species Cucumibius annulatus , recently redescribed from North-West Russia. The draft genome was assembled de novo using DNBSEQ sequencing data (PE300 reads), followed by decontamination and annotation. Final assembly has a size of 73 Mb and a BUSCO completeness score of 87.1%. Comparative genomic analysis against three other tardigrade species ( Hypsibius exemplaris , Ramazzottius varieornatus , and Paramacrobiotus metropolitanus ) revealed unique orthologous gene groups in C. annulatus. We identified significant expansions in protein families associated with stress response, including antioxidant enzymes (e.g., Superoxide Dismutase), chaperones (HSP70), and components of the DNA repair and ubiquitin-proteasome systems. Notably, C. annulatus exhibits a pronounced species-specific expansion of signaling receptors, particularly receptor guanylate cyclases and G-protein coupled receptors, as well as extracellular matrix proteins like metalloproteases. These findings suggest that adaptations in signaling pathways and structural proteins, in addition to typical stress-response genes, may play a crucial role in the survival strategies.