The #endoskeleton formed by the #aciculae and supported by many muscles is quite unique to polychaete annelids and represents the only example outside the #tetrapods of animals with a trunk appendages rigidified by an endoskeleton. Aciculae evolved in stem errant #annelids in the Early #Ordovician indicating the deep ancestry of these structures, predating tetrapod limbs.

We analysed the network in many different ways and found that its structure is quite different from the synaptic #connectome and random networks. One of the interesting findings was that the #aciculae - chitin rods that form an #endoskeleton in the segmental #appendages - are highly connected hubs in the #network and a large number of #muscles is involved in moving them.