| Abstract: | The phylogeny of the Phyllodocidae (Polychaeta Annelida) is examined in an analysis which includes previously unnoticed characters of the nervous system. Concentrating on four problems of importance in understanding the phylogeny of the family, a study of the nervous system demonstrated that: 1. A median antenna, such as that present in species of Eulalia, is not homologous to the nuchal papilla of, for example, Eteone and Phyllodoce; 2. Nuchal organs, presumably found in all phyllodocids, are basically homologous, but four separate types may be recognized; 3. The anterior concentration of the first segments (particularly their tentacular cirri), which is evident in most phyllodocids, is accompanied by different alterations of the ventral nervous system. The polarities of these changes are not self-evident; 4. A study of the ventral nervous system of Eteone reveals that the first apparent segment, bearing two pairs of tentacular cirri, must be regarded as homologous to the second segment of all other phyllodocids. Furthermore, this genus descended from forms in which a segment was present anterior to the first apparent segment, the first two segments possibly bearing tightly packed tentacular cirri. In connection with other characters, this information was used to produce a cladogram, which has some surprising features. The most unexpected result is the prediction that Eteone is the sister group of a taxon containing the genera Paranaitis, Chaetoparia, and Phyllodoce. The results are discussed and compared to those of other investigators. |
