This study provides new insights into the knowledge of the microbiomes associated with the sea star Odontaster validus, a keystone species of Antarctic food webs. We compared the microbiomes of O. validus from different sites of the Weddell Sea and Ross Sea, two areas located in opposite geographical sectors of the Antarctic continent. We also compared microbiomes associated with the seastars and the bacterial assemblages living in the sourrunding sediments, to investigate the origin of these associations.