FIGURE 6. Achaeta singularis sp. nov. A. Juvenile specimen with primordial testis (2) and ovary (3), dorsal view. Dotted areas mark perikarya in brain and ventral nerve cord. The perikarya of the ganglia in II and III are concentrated on the lateral sides. Note nephridia in VI and VII, the oesophageal appendage in V, the dorsal blood vessel in VI, and the winding intestine. From XII on the ganglia are fused among segments; 4: posterior growth zone. The outer pair of postpharyngeal bulbs was not distinguished in this specimen (comp. B). B. Anterior end, lateral view. Perikarya of ventral nerve cord, brain, and prostomial epithelial thickenings are drawn in. Ganglia of II and III are not completely separate, but there is no uniform suboesophageal ganglion over II–IV as in other Achaeta species (comp. Fig. 3B). 1: Prostomial papilla. 2: Oesophageal appendage. 3: Dorsal blood vessel origin. C. Prostomium and first segment, dorsal view. Note the brain, deeply incised anteriorly and posteriorly, and the conspicuous prostomial papillae. Here dotted areas mark the perikarya-free areas. Laterally and posteriad, the prostomial epithelial protrusions gradually merge into the lateral line. D. The brain as seen in living specimens. E. Anterior nephridia, lateral view. - F. Posterior nephridia, ventral view. G. Coelomocytes and piles of rod-shaped structures. D and G are freehand sketches from living specimens, the rest is from stained whole mounts.