Connecting names: Using a micro-CT scanner as a non-destructive method for identification of polyclads (Platyhelminthes: Polycladida)

Abstract

Polyclads are free living marine flatworms that inhabit a great variety of environments, from rocky shore and coral reefs to deep water. Due to their apparent simplicity, polyclads have been mainly classified by their internal reproductive anatomy long with the eyespot’s arrangement, the presence of tentacles and the pharynx type. The study of these characters is often done through histological sectioning which requires obtaining mature specimens, to correctly fixate them and go through several steps before obtaining slides of the reproductive system. This approach is not only time consuming and difficult, but it is destructive. While molecular techniques have been growing in popularity in polyclad research, the availability of them is scarce and sequences still need to be accompanied of specimens’ identification. Micro-CT scanning is considered a nondestructive method to observe internal structures, which also provides the ability for 3D reconstruction of them. Micro-CT imaging has been previously used on the taxonomic studies of invertebrates, including annelids and other flatworm groups. In order to test micro-CT scanning as a tool to match specimens collected around San Juan island intertidal to known species, worms were fixed, pre-stained with Lugol or PTA and mounted in paraffin to be scanned. Internal structures were unclear for all the scans irrespective of the stain used but was generally better for those stained with PTA and embedded in paraffin. Our results show that while feasible there are several aspects that affect CT images results for polyclad identification, leaving room for improvement on the methods used for the imaging.