Spirula spirula is a unique deep-sea squid with unknown taxonomic status. Precise description of shell morphology may help to decide whether the genus contains one or more species. Here, a straight forward description of ontogenetic changes of shell parameters is presented for a single shell of Spirula spirula. Using micro-computed tomography, surface and volumetric data, e.g., chamber volumes and surface areas, as well as siphuncle volumes and surface areas were collected and used for the description. Advantage of the method, combining non-invasive imaging techniques with classical morphometry, is discussed.