Аннотация:A key issue in the study of invertebrate cartilage-like tissues is the absence of a single definition that encompasses their full diversity. Attempts to establish a universal definition of cartilaginous tissue across all Bilateria often lead to the exclusion of certain tissues that could be classified as cartilaginous with only minor adjustments to the criteria. This not only limits their inclusion in specialized reviews but also results in their omission from subsequent studies. Historically, this issue has contributed to the recognition of cartilaginous tissues exclusively within Chordata. Today, this approach has led to hypotheses suggesting independent origins of cartilaginous tissues in different groups of Bilateria. The aim of this review is to propose a new framework for studying cartilage-like tissues in Bilateria by introducing a broad, flexible definition that better accounts for their diversity. Unlike previous studies, this approach emphasizes not only the histological structure of these tissues but also their topological position during ontogeny relative to the overall body plan of the animals. Additionally, it takes into account existing data on structural and regulatory genes involved in the formation of these tissues. This perspective enables a more comprehensive analysis of the evolutionary origins and development of cartilage-like tissues. In particular, this approach supports the hypothesis that, at least in Spiralia, structures composed of cartilage-like tissues may share a common tissue ancestor, as they are topologically associated with central elements of the nervous system in addition to previously recognized shared characteristics, such as histological structure and matrix components. The review found no evidence contradicted this hypothesis; however, several supporting arguments were identified. A common origin of these structures across all Bilateria also remains plausible, suggesting the approach not only systematizes existing knowledge but also advances hypotheses on the evolution of cartilage-like tissues in Bilateria.
