Three-dimensional analysis of the canal network of an Indonesian Stylaster (Cnidaria, Hydrozoa, Stylasteridae) by means of X-ray computed microtomography

This study describes the architecture of the coenosteal network in an Indonesian Stylaster species investigated by means of the X-ray computed microtomography (μ-CT) technique. The 3D approach allowed to characterize all internal cavity structures: a network of thin canals, gastropores, dactylopores, and ampullae. The main feature highlighted by this reconstruction is a dense network of thin canals extended to the entire colony. This network gives rise to and surrounds each cyclosystem. Moreover, the 3D analysis made it possible to study the reciprocal relationship between adjacent cyclosystems and to hypothesize the growth process of the branches of Stylaster sp.: each new cyclosystem buds between the gastropore and the dactylopores of the last formed one. The dactylopores of each cyclosystem are partially derived from the precedent one and are partially newly formed. The thin canals enveloping the dactylopores are actively involved in both the formation of a new gastropore and in the re-establishment of the typical amount of dactylopores in each cyclosystem. This growth process was confirmed by the scanning electron microscopy (SEM) observations of apical cyclosystems of several specimens. Results indicate that the non-destructive X-ray μ-CT technique can be fruitfully applied to characterize the coenosteal structures of stylasterids allowing the repetitive study of a specimen by means of virtually infinite section planes and different kinds of analyses (e. g., channel width and porosity).