An international research team was the first to describe the treelike internal anatomy of a symbiotic worm and sponge. She discovered host sponges and their guest worms in a remote area of Darwin, Australia, where these animals live. They collected samples, some of which are now in the collections of the Biodiversity Museum at the University of Göttingen.
The marine worm Ramisyllis multicaudata, which lives in the internal canals of the sponge, has a branched body with one head and many posterior ends. An international research team has described the internal anatomy of this intriguing animal. The researchers found that the complex body of this worm spreads widely in the channels of the host sponges. In addition, they describe the anatomical details and nervous system of her unusual reproductive units, stolons, which, when disconnected for fertilization, form their own brains, allowing them to navigate their environment.
For their analysis, they combined methods such as histology, electron-optical microscopy, immunohistochemistry, confocal laser microscopy, and X-ray computed microtomography. This made it possible to obtain three-dimensional images of both the various internal organs of the worms and the interior of the sponges in which they live. Scientists show that when the body of these animals divides, all of their internal organs divide, which has never been seen before.
Three-dimensional models made it possible to find a new anatomical structure that is characteristic only of these animals. It is formed by muscle bridges that cross between different organs whenever their body needs to form a new branch. These muscle bridges are important because they confirm that the bifurcation process does not occur early in life, but only when worms become adults and then throughout their lives. In addition, the researchers suggest that this unique “fingerprint” of muscle bridges can theoretically distinguish the original branch from the new one in each bifurcation of the complex body network.
This new study examines the anatomy of the reproductive units (stolons) that develop at the rear ends of the body when these animals are about to reproduce, and which are characteristic of the family to which they belong (Syllidae). The results show that these stolons form a new brain and have their own eyes. This allows them to navigate their environment as they are separated from the body for fertilization. This brain is connected to the rest of the nervous system by a nerve ring that surrounds the intestines.
This study solves some of the mysteries that these curious animals have been posing since the first branched ringlet was discovered at the end of the 19th century. Scientists concluded that the intestines of these animals may be functional, but they never found traces of food in it. Therefore, scientists do not understand how they can feed their huge ramified bodies.