Integrated transcriptomic and histological insights into immune and stress-related pathways in the Antarctic sea anemone Urticinopsis antarctica

Antarctic sea anemones are dominant benthic predators, yet their molecular adaptive strategies to polar environments remain poorly understood. Urticinopsis antarctica is one of the most abundant Antarctic actiniarians, but until now it has lacked any integrated molecular characterisation This study provides the first comprehensive analysis combining de novo transcriptomics with histological and cytological observations to investigate immune and stress-response mechanisms in this azooxanthellate anthozoan. Gene Ontology and Pfam-based analyses revealed a broad and evolutionarily conserved innate immune repertoire, including Toll-like receptor, NF-κB, JAK–STAT and NOD-like receptor pathways, together with numerous transcripts of pattern-recognition domains such as TIR, NACHT, LRR and C-type lectins. Integration with signal peptide prediction demonstrated a significant enrichment of immune- and stress-related genes within the secretome, indicating a strong bias toward extracellular defence strategies. Histological analyses revealed a typical a diploblastic organization with abundant cnidocytes, mucous cells and migratory amoeboid cells, consistent with an epithelial-centred immune system. The absence of algal symbionts was confirmed at both molecular and tissue levels. Together, these findings indicate that U. antarctica maintains a complex, flexible immune and stress-response architecture despite extreme thermal stability and resource limitation. This new molecular and cellular baseline establishes U. antarctica as a valuable reference for understanding resilience, cold adaptation, and the evolution of immunity in polar anthozoans, and provides a foundation for future functional and experimental work on the responses of Antarctic benthic species to environmental change.