Аннотация:The annelid nervous system has long been known to encompass a greater variety than many other evolutionary lineages, however,
neurophylogenetic studies testing the homology and evolution of these multiple neural traits have never been carried out in
the Annelida. The Siboglinidae nervous system is, with a ventrally positioned brain and indistinct segmentation of the anterior
body, highly deviant from other annelids and its origin is still questioned. Central for understanding the nervous system of these
endosymbiont-housing, generally gutless, tubeworms is the bone-devouring Osedax; the nervous traits of which are here mapped and their evolution traced across Siboglinidae. The four examined female Osedax spp. and the bone-eating O. priapus male
all showed a simple nervous system, comprising a ventral brain with several commissures connected with anteriorly directed
paired palp and gonoduct nerves, and four main pairs of posteriorly directed longitudinal nerves. A broader comparison across
Siboglinidae suggests new homologies of the ambiguous, and much debated, anterior segments - with the trunk of Osedax females
(and O. priapus males) suggested to comprise two segments and Osedax dwarf males suggested to have three body segments in
total. However, besides from additional lateral and dorsal longitudinal nerves and details of the brain only described for Osedax, this
first neural character reconstruction reveals that the intraepidermal nervous system with multiple, widely separated nerve cords,
double brain commissures, and double palp nerves of Osedax are all siboglinid plesiomorphies; hereby bridging the evolutionary
gap to non-siboglinid annelids and enhancing our understanding of the neural evolution within Siboglinidae.