We characterized six tintinnid ciliates from Antarctic waters using molecular markers and morphological traits: Amphorellopsis quinquealata , Codonellopsis gaussi , Cymatocylis convallaria , Cy. calyciformis , Cy. drygalskii, and Laackmanniella prolongata . The 100% similarity in SSU-ITS1-5.8S rDNA -ITS2-partial LSU rDNA sequences among Cy. convallaria , Cy. calyciformis, and Cy. drygalskii is supportive of synonymy. Codonellopsis gaussi and L. prolongata also showed high levels of similarity in SSU rDNA (99.83%) and the D2 domain of LSU rDNA (95.77%), suggesting that they are closely related. Phylogenetic analysis placed Cymatocylis in the Rhabdonellidae, Amphorellopsis in the Tintinnidae and L. prolongata/Co. gaussi within the Dictyocystidae.