Integrative anatomical study of the branched annelid <i>Ramisyllis multicaudata</i> (Annelida, Syllidae)

The sponge-dwelling Syllidae Ramisyllis multicaudata and Syllis ramosa are the only annelid species for which a branched body with one head multiple posterior ends is known. In these species, located deep within sponge, branches extend through canal system of their host. morphology creatures has captivated biologists since they were first discovered in late XIXth century, external characteristics have been well documented. However, how bodies fit symbiotic host sponges translate into internal anatomy not documented before. These features crucially relevant understanding animals, therefore, aim this study was to investigate aspects. order assess questions, live observation, as wells histology, immunohistochemistry, micro-computed tomography, transmission electron microscopy techniques used on specimens R. multicaudata. By using techniques, we show that complex extends greatly sponges. We demonstrate iterative bifurcation accompanied by longitudinal organ systems characteristic annelids. Additionally, also highlight process leaves an unmistakable fingerprint form newly-described “muscle bridges.” structures theoretically allow distinguish original derived at each bifurcation. Last, characterize some anatomical stolons (reproductive units) multicaudata, particularly nervous system. Here, provide annelid. This information crucial deepen our animals biology, but it will be key inform future studies try explain evolved.