First evaluation of contrast-enhanced micro-XCT as a tool for organismal and reproductive trait observations in corals based on scans of Thesea nivea Deichmann, 1936

Micro-X-ray computed tomography (micro-XCT) with contrast enhancement is considered a non-destructive tool that is increasingly being applied to explore the internal and external structures of vertebrates and invertebrates. Although micro-XCT has been applied to corals to study skeletal features, contrast enhancement has not been applied to evaluate the utility for visualization of soft tissue structures in corals. This study is the first to evaluate the utility of contrast enhancement to visualize internal and external features, including soft tissue features, of octocorals. Contrast staining of a Thesea nivea specimen with 2.5% Lugol's iodine permitted visualization of soft tissues with sufficient density differences among tissues to distinguish skeletal elements, dermal layers, polyp internal structures, and oocyte stages and features. Thus, contrast-enhanced micro-XCT is a tool that could advance octocoral systematics. Further optimization of this approach could further enhance its utility for systematics and increase its efficiency through development of semi-automated pipelines for morphometric and histological analyses.