Note
Interspecific variation was examined in six species of Capitella (sp. I, la, II, III, IlIa and ORLEANS) from the Woods Hole region with respect to genital spine, sperm and larval morphology. The stability of spine number in the eighth and ninth thoracic setigers was examined and found to reach a maximum value at an early age in setiger 9. Spine number showed greater variability in setiger 8 although the number in the oldest animals studied appeared to reach a maximum value. Genital spine number and morphology should be included in future descriptions of Capitella species.