Figure 7

Phylogenetic distribution of serotonin immunoreactive perikarya and peripheral nerve patterns. A) Reconstruction of the basal architecture of a trunk ventral ganglion across clitellate groups, based on this study and previous reports [20,27,29,32,35,36]. Colored circles represent serotonin immunoreactive perikarya, with color representing putative homologous groups; A to G cells in Crassiclitellata refer to cell groups defined for Lumbricus terrestris [35]; anteromedial (am), dorsolateral (dl), ventrolateral (vl), posteromedial (pm) and Retzius cells in Hirudina refer to cell groups defined for leech species [27,29,32]. Segmental peripheral nerves are shown aligned according to their position along the ganglion. B) Phylogenetic mapping of the number of segmental peripheral nerves across Annelida, and maximum likelihood estimations of the ancestral state at each node. Pie charts illustrate the relative likelihood of a given node having had each character state, and were calculated in R [63] using the ace function from the ape package [64]. Annelid relationships are based on recent phylogenetic studies [50,52]. Labeled ancestral nodes are for Errantia (E) polychaetes, Sedentaria (S) polychaetes and Clitellata (C); the dashed box highlights data from this paper. Nerve number for each group is based on information from one or a few species, except for Naididae, where ancestral condition was estimated from our 12 study species. References are indicated on the right, in brackets for published works; *: data from this study; **R. Hessling, personal communications in [7]; ***E.E. Zattara, unpublished observations.