The Shaenor was a late 24th century Romulan Imperial scout ship operated by the Tal Shiar.
The ship was transporting twenty-six passengers, including Ramdha, when it encountered a Borg cube and was assimilated in the 2380s. It was the last ship assimilated by the cube before it suffered a submatrix collapse. (PIC: "Absolute Candor")
To the best of the knowledge of the operational head of the Borg Reclamation Project, Hugh, the ship's complement comprised the only known Romulans ever assimilated by the Borg Collective. (PIC: "The End is the Beginning", "Broken Pieces")
This scout ship was only mentioned in dialogue.
Hugh was apparently not aware of at least two other Romulans assimilated by the Borg, including Orum and another individual.