Comparative schemes of the sensory inputs and motor outputs to emphasize the functional subdivisions. The tuft type sensory cells and their inputs are characterized for alvinellid worms. The two distinct tuft type cells on the head or prostomium are identified. Note that the branchial crown of Terebellida (Paralvinella) is not homologous to those of Serpulidae and palps of Nereididae. Some neural pathways are not precisely identified. Data are simplified from Orrhage and Müller . bt, bud type cell; lt, line type; ss, sensilla type; tt, tuft type; VNC, subesophageal ganglia with ventral nerve cord/ganglia.