The folders GMPKU2311, GMPKU3089, ELISN108-343 and ELISN31-5 contain data from X-ray tomographic analyses of fossil embryos and post-embryonic stages as described: There is one data folder provided for each specimen, each containing the following: - Raw data: zip archive containing the raw scan data (.tif image stack). - Working files: zip archive containing the segmented slices (.tif image stack exported from Avizo labels). - Avizo project: the Avizo .hx project file. - Avizo labels: the Avizo .am labels file, containing the segmentation information. - 3D model: the 3D surface computed from the segmented labels data (.stl file). In the case of GMPKU2311 only the raw data and 3D model file are provided, as the surface was computed directly from an isosurface of the specimen in Avizo. The individual slices (.tif images) can be viewed with standard graphics software, and the datasets can be studied in 3D using tomographic reconstruction software such as Avizo (www.vsg3d.com/), Spiers (www.spiers-software.org/), VG Studio Max (www.volumegraphics.com) etc. The Avizo project and label files (.hx and .am files) require Avizo software (www.vsg3d.com/) to be opened. The 3D models (.stl files) are widely compatible with 3D freeware packages such as MeshLab (http://meshlab.sourceforge.net/) or Blender (https://www.blender.org/), or with proprietary software, e.g. Avizo (www.vsg3d.com/), Geomagic (http://www.geomagic.com/en/), Mimics (http://biomedical.materialise.com/mimics). The files relate to the following publication: Dong, X.; Vargas, K.; Cunningham, J. A.; Zhang, H.; Liu, T.; Chen, F.; Liu, J.; Bengtson, S. & Donoghue, P. C. J. 2015. Developmental biology of the early Cambrian cnidarian Olivooides. Journal of Paleontology.