Fig. 4. Reconstruction and schematic reconstructions of annelid nervous systems plotted on a simplified phylogeny.

(A) Reconstruction by M. Collins © Royal Ontario Museum, all rights reserved (see also movie S1). (B) Simplified phylogeny of Annelida with C. spinosa recovered in the annelid stem group (see also the Supplementary Materials for the full phylogenetic results). Topology is based on the analysis using phylogenetic constraints based on recent phylogenomic trees. Proposed nervous system synapomorphies are shown at nodes, and inferred losses are shown along branches as cross marks. cc, circumoral connectives; ga, segmental ganglion; ma, median antenna; pan, parapodial nerve; pa, palp; sn, segmental nerve; sog, supraesophegeal ganglion; vnc, ventral nerve cord.