Sample POS455-C1W originates from Sula reef, off Norway, where it was taken with the submersible Jago during Poseidon cruise POS455 (position: 64.1110°N, 8.1187°E, 303 m water depth; white colourmorph). The coral colony fragment was scanned by a Toshiba Aquilion 64 computer tomograph (CT) at the hospital Klinikum Bremen-Mitte with an x-ray source voltage of 120 kV and a current of 600 mA. The CT image stack has a resolution of 0.35 mm in x-direction and y-direction and 0.5 mm resolution in z-direction (0.3 mm reconstruction unit). Images were reconstructed using Toshiba's patented helical cone beam reconstruction technique (TCOT) and are provided in DICOM-format.This dataset contains the CT raw data (C1W_RawData) and the polyp-cavity instance segmentation (C1W_polyp-cavity-segmentation).