Meeting Abstract
Still unplaced, Lobatocerebrum (Lobatocerebridae, Spiralia incertae sedis) is one of the most enigmatic bilaterian left. It was described in 1980 by Reinhard Rieger as an unsegmented, completely ciliated, thin and 2 mm long interstitial worm lacking any form of appendages or bristles, but possessing a glandular cuticle, a ventral mouth and through gut. Detailed LM and TEM studies revealed a range of apomorphies such as a large multilobed brain as well as similarities to Platyhelminthes and Annelida. However, after 30 years we still haven’t been able to resolve its exact position in Spiralia. With ongoing studies of new material employing phylogenomic analyses and detailed morphological reconstructions we hope to get closer to an answer. The last decades of research have accumulated a much broader knowledge on the spiralian nervous system, mainly facilitated by the progresses in immunohistochemistry and confocal laser scanning microscopy. With these techniques we have now collected comparative data on the Lobatocerebrum muscle- and nervous system, showing several previously undiscovered features such as a mid-ventral nerve, a third trunk commissure, and specific neurotransmitter patterns. Furthermore, we were able to confirm many of the discoveries of R. Rieger as well as unravel the detailed architecture of, e.g. the brain commissures, nerve cords emerging from the brain lobes and the muscular layout. Possible plesiomorphies and synapomorphies with Nemertea, Platyhelminthes, Gastrotricha and Annelida are discussed relative to the new phylogenomic spiralian tree topology, and various evolutionary scenarios of the neuro-muscular systems are presented.
